[Furtherthesamepassageservesforurineandsemen；andwhateveranimalshavebothkindsofexcrement，thatofliquidandthatofsolidnutriment，dischargethesemenbythesamepassageastheliquidexcrement（foritisasecretionofaliquid，sincethenutrimentofallanimalsisratherliquidthansolid），butthosewhichhavenoliquidexcrementdischargeitatthepassageofthesolidresidua。Moreover，waste—productsarealwaysmorbid，buttheremovalofthesecretionisuseful；nowthedischargeofthesemenparticipatesinbothcharacteristicsbecauseittakesupsomeofthenon—usefulnutriment。Butifitwereawaste—productitwouldbealwaysharmful；asitis，itisnotso。]
　　Fromwhathasbeensaid，itisclearthatsemenisasecretionofusefulnutriment，andthatinitslaststage，whetheritisproducedbyallorno。
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　　Afterthiswemustdistinguishofwhatsortofnutrimentitisasecretion，andmustdiscussthecatameniawhichoccurincertainofthevivipara。Forthusweshallmakeitclear（1）whetherthefemalealsoproducessemenlikethemaleandthefoetusisasinglemixtureoftwosemens，orwhethernosemenissecretedbythefemale，and，（2）
　　ifnot，whethershecontributesnothingelseeithertogenerationbutonlyprovidesareceptacle，orwhethershedoescontributesomething，and，ifso，howandinwhatmannershedoesso。
　　Wehavepreviouslystatedthatthefinalnutrimentisthebloodinthesanguineaandtheanalogousfluidintheotheranimals。Sincethesemenisalsoasecretionofthenutriment，andthatinitsfinalstage，itfollowsthatitwillbeeither（1）bloodorthatwhichisanalogoustoblood，or（2）somethingformedfromthis。Butsinceitisfromtheblood，whenconcoctedandsomehowdividedup，thateachpartofthebodyismade，andsincethesemenifproperlyconcoctedisquiteofadifferentcharacterfromthebloodwhenitisseparatedfromit，butifnotproperlyconcoctedhasbeenknowninsomecasestoissueinabloodyconditionifoneforcesoneselftoooftentocoition，thereforeitisplainthatsemenwillbeasecretionofthenutrimentwhenreducedtoblood，beingthatwhichisfinallydistributedtothepartsofthebody。Andthisisthereasonwhyithassogreatpower，forthelossofthepureandhealthybloodisanexhaustingthing；forthisreasonalsoitisnaturalthattheoffspringshouldresembletheparents，forthatwhichgoestoallthepartsofthebodyresemblesthatwhichisleftover。Sothatthesemenwhichistoformthehandorthefaceorthewholeanimalisalreadythehandorfaceorwholeanimalundifferentiated，andwhateachofthemisactuallysuchisthesemenpotentially，eitherinvirtueofitsownmassorbecauseithasacertainpowerinitself。
　　Imentionthesealternativesherebecausewehavenotyetmadeitclearfromthedistinctionsdrawnhithertowhetheritisthematterofthesementhatisthecauseofgeneration，orwhetherithasinitsomefacultyandefficientcausethereof，forthehandalsooranyotherbodilypartisnothandorotherpartinatruesenseifitbewithoutsoulorsomeotherpower，butisonlycalledbythesamenameasthelivinghand。
　　Onthissubject，then，somuchmaybelaiddown。Butsinceitisnecessary（1）thattheweakeranimalalsoshouldhaveasecretiongreaterinquantityandlessconcocted，and（2）thatbeingofsuchanatureitshouldbeamassofsanguineousliquid，and（3）sincethatwhichNatureendowswithasmallerportionofheatisweaker，and（4）sinceithasalreadybeenstatedthatsuchisthecharacterofthefemale—puttingalltheseconsiderationstogetherweseethatthesanguineousmatterdischargedbythefemaleisalsoasecretion。Andsuchisthedischargeoftheso—calledcatamenia。
　　Itisplain，then，thatthecatameniaareasecretion，andthattheyareanalogousinfemalestothesemeninmales。Thecircumstancesconnectedwiththemareevidencethatthisviewiscorrect。Forthesemenbeginstoappearinmalesandtobeemittedatthesametimeoflifethatthecatameniabegintoflowinfemales，andthattheychangetheirvoiceandtheirbreastsbegintodevelop。So，too，inthedeclineoflifethegenerativepowerfailsintheonesexandthecatameniaintheother。
　　Thefollowingsignsalsoindicatethatthisdischargeinfemalesisasecretion。Generallyspeakingwomensufferneitherfromhaemorrhoidsnorbleedingatthenosenoranythingelseofthesortexceptwhenthecatameniaareceasing，andifanythingofthekindoccurstheflowisinterferedwithbecausethedischargeisdivertedtoit。
　　Further，theblood—vesselsofwomenstandoutlessthanthoseofmen，andwomenarerounderandsmootherbecausethesecretionwhichinmengoestothesevesselsisdrainedawaywiththecatamenia。Wemustsuppose，too，thatthesamecauseaccountsforthefactthatthebulkofthebodyissmallerinfemalesthaninmalesamongthevivipara，sincethisistheonlyclassinwhichthecatameniaaredischargedfromthebody。Andinthisclassthefactisclearestinwomen，forthedischargeisgreaterinwomenthanintheotheranimals。Whereforeherpallorandtheabsenceofprominentblood—vesselsismostconspicuous，andthedeficientdevelopmentofherbodycomparedwithaman’sisobvious。
　　Nowsincethisiswhatcorrespondsinthefemaletothesemeninthemale，andsinceitisnotpossiblethattwosuchdischargesshouldbefoundtogether，itisplainthatthefemaledoesnotcontributesementothegenerationoftheoffspring。Forifshehadsemenshewouldnothavethecatamenia；but，asitis，becauseshehasthelattershehasnottheformer。
　　Ithasbeenstatedthenthatthecatameniaareasecretionasthesemenis，andconfirmationofthisviewmaybedrawnfromsomeofthephenomenaofanimals。Forfatcreaturesproducelesssementhanleanones，asobservedbefore。Thereasonisthatfatalso，likesemen，isasecretion，isinfactconcoctedblood，onlynotconcoctedinthesamewayasthesemen。Thus，ifthesecretionisconsumedtoformfatthesemenisnaturallydeficient。Andsoamongthebloodlessanimalsthecephalopodaandcrustaceaareinbestconditionaboutthetimeofproducingeggs，for，becausetheyarebloodlessandnofatisformedinthem，thatwhichisanalogousinthemtofatisatthatseasondrawnofftoformthespermaticsecretion。
　　Andaproofthatthefemaledoesnotemitsimilarsementothemale，andthattheoffspringisnotformedbyamixtureofboth，assomesay，isthatoftenthefemaleconceiveswithoutthesensationofpleasureinintercourse，andifagainthepleasureisexperiencebyhernolessthanbythemaleandthetwosexesreachtheirgoaltogether，yetoftennoconceptiontakesplaceunlesstheliquidoftheso—calledcatameniaispresentinarightproportion。Hencethefemaledoesnotproduceyoungifthecatameniaareabsentaltogether，noroftenwhen，theybeingpresent，theeffluxstillcontinues；butshedoessoafterthepurgation。Forintheonecaseshehasnotthenutrimentormaterialfromwhichthefoetuscanbeframedbythepowercomingfromthemaleandinherentinthesemen，andintheotheritiswashedawaywiththecatameniabecauseoftheirabundance。Butwhenaftertheiroccurrencethegreaterparthasbeenevacuated，theremainderisformedintoafoetus。Casesofconceptionwhenthecatameniadonotoccuratall，orofconceptionduringtheirdischargeinsteadofafterit，areduetothefactthatintheformerinstancethereisonlysomuchliquidtobeginwithasremainsbehindafterthedischargeinfertilewomen，andnogreaterquantityissecretedsoastocomeawayfromthebody，whileinthelatterinstancethemouthoftheuterusclosesafterthedischarge。When，therefore，thequantityalreadyexpelledfromthebodyisgreatbutthedischargestillcontinues，onlynotonsuchascaleastowashawaythesemen，thenitisthatconceptionaccompaniescoition。Norisitatallstrangethatthecatameniashouldstillcontinueafterconception（forevenafterittheyrecurtosomeextent，butarescantyanddonotlastduringalltheperiodofgestation；this，however，isamorbidphenomenon，whereforeitisfoundonlyinafewcasesandthenseldom，whereasitisthatwhichhappensasaregularthingthatisaccordingtoNature）。
　　Itisclearthenthatthefemalecontributesthematerialforgeneration，andthatthisisinthesubstanceofthecatamenia，andthattheyareasecretion。
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　　Somethinkthatthefemalecontributessemenincoitionbecausethepleasuresheexperiencesissometimessimilartothatofthemale，andalsoisattendedbyaliquiddischarge。Butthisdischargeisnotseminal；itismerelypropertothepartconcernedineachcase，forthereisadischargefromtheuteruswhichoccursinsomewomenbutnotinothers。Itisfoundinthosewhoarefair—skinnedandofafemininetypegenerally，butnotinthosewhoaredarkandofamasculineappearance。Theamountofthisdischarge，whenitoccurs，issometimesonadifferentscalefromtheemissionofsemenandfarexceedsit。Moreover，differentkindsoffoodcauseagreatdifferenceinthequantityofsuchdischarges；forinstancesomepungently—flavouredfoodscausethemtobeconspicuouslyincreased。
　　Andastothepleasurewhichaccompaniescoitionitisduetoemissionnotonlyofsemen，butalsoofaspiritus，thecomingtogetherofwhichprecedestheemission。Thisisplaininthecaseofboyswhoarenotyetabletoemitsemen，butareneartheproperage，andofmenwhoareimpotent，forallthesearecapableofpleasurebyattrition。Andthosewhohavebeeninjuredinthegenerativeorganssometimessufferfromdiarrhoeabecausethesecretion，whichtheyarenotabletoconcoctandturnintosemen，isdivertedintotheintestine。Nowaboyislikeawomaninform，andthewomanisasitwereanimpotentmale，foritisthroughacertainincapacitythatthefemaleisfemale，beingincapableofconcoctingthenutrimentinitslaststageintosemen（andthisiseitherbloodorthatwhichisanalogoustoitinanimalswhicharebloodlessowingtothecoldnessoftheirnature）。Asthendiarrhoeaiscausedinthebowelsbytheinsufficientconcoctionoftheblood，soarecausedintheblood—vesselsalldischargesofblood，includingthatofthecatamenia，forthisalsoissuchadischarge，onlyitisnaturalwhereastheothersaremorbid。
　　Thusitisclearthatitisreasonabletosupposethatgenerationcomesfromthis。Forthecatameniaaresemennotinapurestatebutinneedofworkingup，asintheformationoffruitsthenutrimentispresent，whenitisnotyetsiftedthoroughly，butneedsworkinguptopurifyit。Thusthecatameniacausegenerationmixturewiththesemen，asthisimpurenutrimentinplantsisnutritiouswhenmixedwithpurenutriment。
　　Andasignthatthefemaledoesnotemitsemenisthefactthatthepleasureofintercourseiscausedbytouchinthesameregionofthefemaleasofthemale；andyetisitnotfromthencethatthisflowproceeds。Further，itisnotallfemalesthathaveitatall，butonlythesanguinea，andnotallevenofthese，butonlythosewhoseuterusisnotnearthehypozomaandwhichdonotlayeggs；itisnotfoundintheanimalswhichhavenobloodbutonlytheanalogousfluid（forwhatisbloodintheformerisrepresentedbyanotherfluidinthelatter）。Thereasonwhyneitherthelatternorthosesanguineamentioned（i。e。thosewhoseuterusislowandwhichdonotlayeggs）
　　havethiseffluxionisthedrynessoftheirbodies；thisallowsbutlittlemattertobesecreted，onlyenoughforgenerationbutnotenoughtobedischargedfromthebody。Allanimalsthatareviviparouswithoutproducingeggsfirst（sucharemanandallquadrupedswhichbendtheirhind—legsoutwards，foralltheseareviviparouswithoutproducingeggs）—allthesehavethecatamenia，unlesstheyaredefectiveindevelopmentasthemule，onlytheeffluxisnotabundantasinwomen。DetailsofthefactsineachanimalhavebeengivenintheEnquiriesconcerninganimals。
　　Thecatameniaaremoreabundantinwomenthanintheotheranimals，andmenemitthemostsemeninproportiontotheirsize。
　　Thereasonisthatthecompositionoftheirbodiesisliquidandhotcomparedtoothers，formoremattermustbesecretedinsuchacase。
　　Further，manhasnosuchpartsinhisbodyasthosetowhichthesuperfluousmatterisdivertedintheotheranimals；forhehasnogreatquantityofhairinproportiontohisbody，noroutgrowthsofbones，horns，andteeth。
　　Thereisevidencethatthesemenisinthecatamenia，for，assaidbefore，thissecretionappearsinthemaleatthesametimeoflifeasthecatameniainthefemale；thisindicatesthatthepartsdestinedtoreceiveeachofthesesecretionsaredifferentiatedatthesametimeinbothsexes；andastheneighboringpartsinbothbecomeswollenthehairofpubertyspringsforthinbothalike。Asthepartsinquestionareonthepointofdifferentiatingtheyaredistendedbythespiritus；thisisclearerinmalesinthetestes，butappearsalsoaboutthebreasts；infemalesitismoremarkedinthebreasts，foritiswhentheyhaverisentwofingers’breadththatthecatameniagenerallybegin。
　　Now，inalllivingthingsinwhichthemaleandfemalearenotseparatedthesemen（orseed）isasortofembryo；byembryoI
　　meanthefirstmixtureofmaleandfemale；hence，fromonesemencomesonebodys—forexample，onestalkofwheatfromonegrain，asoneanimalfromoneegg（fortwineggsarereallytwoeggs）。Butinwhateverkindsthesexesaredistinguished，inthesemanyanimalsmaycomefromoneemissionofsemen，showingthatthesemendiffersinitsnatureinplantsandanimals。Aproofofthisisthatanimalswhichcanbearmorethanoneyoungoneatatimedosoinconsequenceofonlyonecoition。Whereby，too，itisplainthatthesemendoesnotcomefromthewholeofthebody；forneitherwouldthedifferentpartsofthesemenalreadybeseparatedassoonasdischargedfromthesamepart，norcouldtheybeseparatedintheuterusiftheyhadonceentereditalltogether；butwhatdoeshappenisjustwhatonewouldexpect，sincewhatthemalecontributestogenerationistheformandtheefficientcause，whilethefemalecontributesthematerial。Infact，asinthecoagulationofmilk，themilkbeingthematerial，thefig—juiceorrennetisthatwhichcontainsthecurdlingprinciple，soactsthesecretionofthemale，beingdividedintopartsinthefemale。Whyitissometimesdividedintomoreorfewerparts，andsometimesnotdividedatall，willbethesubjectofanotherdiscussion。Butbecauseitdoesnotdifferinkindatanyratethisdoesnotmatter，butwhatdoesmatterisonlythateachpartshouldcorrespondtothematerial，beingneithertoolittletoconcoctitandfixitintoform，nortoomuchsoastodryitup；itthengeneratesanumberofoffspring。Butfromthisfirstformativesemen，ifitremainsone，andisnotdivided，onlyoneyoungonecomesintobeing。
　　That，then，thefemaledoesnotcontributesementogeneration，butdoescontributesomething，andthatthisisthematterofthecatamenia，orthatwhichisanalogoustoitinbloodlessanimals，isclearfromwhathasbeensaid，andalsofromageneralandabstractsurveyofthequestion。Fortheremustneedsbethatwhichgeneratesandthatfromwhichitgenerates；evenifthesebeone，stilltheymustbedistinctinformandtheiressencemustbedifferent；andinthoseanimalsthathavethesepowersseparateintwosexesthebodyandnatureoftheactiveandthepassivesexmustalsodiffer。If，then，themalestandsfortheeffectiveandactive，andthefemale，consideredasfemale，forthepassive，itfollowsthatwhatthefemalewouldcontributetothesemenofthemalewouldnotbesemenbutmaterialforthesementoworkupon。Thisisjustwhatwefindtobethecase，forthecatameniahaveintheirnatureanaffinitytotheprimitivematter。
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　　Somuchforthediscussionofthisquestion。Atthesametimetheanswertothenextquestionwehavetoinvestigateisclearfromtheseconsiderations，Imeanhowitisthatthemalecontributestogenerationandhowitisthatthesemenfromthemaleisthecauseoftheoffspring。Doesitexistinthebodyoftheembryoasapartofitfromthefirst，minglingwiththematerialwhichcomesfromthefemale？Ordoesthesemencommunicatenothingtothematerialbodyoftheembryobutonlytothepowerandmovementinit？Forthispoweristhatwhichactsandmakes，whilethatwhichismadeandreceivestheformistheresidueofthesecretioninthefemale。Nowthelatteralternativeappearstobetherightonebothaprioriandinviewofthefacts。For，ifweconsiderthequestionongeneralgrounds，wefindthat，wheneveronethingismadefromtwoofwhichoneisactiveandtheotherpassive，theactiveagentdoesnotexistinthatwhichismade；and，stillmoregenerally，thesameapplieswhenonethingmovesandanotherismoved；themovingthingdoesnotexistinthatwhichismoved。Butthefemale，asfemale，ispassive，andthemale，asmale，isactive，andtheprincipleofthemovementcomesfromhim。Therefore，ifwetakethehighestgeneraunderwhichtheyeachfall，theonebeingactiveandmotiveandtheotherpassiveandmoved，thatonethingwhichisproducedcomesfromthemonlyinthesenseinwhichabedcomesintobeingfromthecarpenterandthewood，orinwhichaballcomesintobeingfromthewaxandtheform。Itisplainthenthatitisnotnecessarythatanythingatallshouldcomeawayfromthemale，andifanythingdoescomeawayitdoesnotfollowthatthisgivesrisetotheembryoasbeingintheembryo，butonlyasthatwhichimpartsthemotionandastheform；
　　sothemedicalartcuresthepatient。
　　Thisaprioriargumentisconfirmedbythefacts。Foritisforthisreasonthatsomemaleswhichunitewiththefemaledonot，itappears，insertanypartofthemselvesintothefemale，butonthecontrarythefemaleinsertsapartofherselfintothemale；thisoccursinsomeinsects。Fortheeffectproducedbythesemeninthefemale（inthecaseofthoseanimalswhosemalesdoinsertapart）isproducedinthecaseoftheseinsectsbytheheatandpowerinthemaleanimalitselfwhenthefemaleinsertsthatpartofherselfwhichreceivesthesecretion。Andthereforesuchanimalsremainunitedalongtime，andwhentheyareseparatedtheyoungareproducedquickly。Fortheunionlastsuntilthatwhichisanalogoustothesemenhasdoneitswork，andwhentheyseparatethefemaleproducestheembryoquickly；
　　fortheyoungisimperfectinasmuchasallsuchcreaturesgivebirthtoscoleces。
　　Whatoccursinbirdsandoviparousfishesisthegreatestproofthatneitherdoesthesemencomefromallpartsofthemalenordoesheemitanythingofsuchanatureastoexistwithinthatwhichisgenerated，aspartofthematerialembryo，butthatheonlymakesalivingcreaturebythepowerwhichresidesinthesemen（aswesaidinthecaseofthoseinsectswhosefemalesinsertapartofthemselvesintothemale）。Forifahen—birdisinprocessofproducingwind—eggsandisthentroddenbythecockbeforetheegghasbeguntowhitenandwhileitisallstillyellow，thentheybecomefertileinsteadofbeingwind—eggs。Andifwhileitisstillyellowshebetroddenbyanothercock，thewholebroodofchicksturnoutlikethesecondcock。Hencesomeofthosewhoareanxioustorearfinebirdsactthus；theychangethecocksforthefirstandsecondtreading，notasiftheythoughtthatthesemenismingledwiththeeggorexistsinit，orthatitcomesfromallpartsofthecock；forifitdiditwouldhavecomefrombothcocks，sothatthechickwouldhaveallitspartsdoubled。Butitisbyitsforcethatthesemenofthemalegivesacertainqualitytothematerialandthenutrimentinthefemale，forthesecondsemenaddedtothefirstcanproducethiseffectbyheatandconcoction，astheeggacquiresnutrimentsolongasitisgrowing。
　　Thesameconclusionistobedrawnfromthegenerationofoviparousfishes。Whenthefemalehaslaidhereggs，themalespinklesthemiltoverthem，andthoseeggsarefertilizedwhichitreaches，butnottheothers；thisshowsthatthemaledoesnotcontributeanythingtothequantitybutonlytothequalityoftheembryo。
　　Fromwhathasbeensaiditisplainthatthesemendoesnotcomefromthewholeofthebodyofthemaleinthoseanimalswhichemitit，andthatthecontributionofthefemaletothegenerativeproductisnotthesameasthatofthemale，butthemalecontributestheprincipleofmovementandthefemalethematerial。Thisiswhythefemaledoesnotproduceoffspringbyherself，forsheneedsaprinciple，i。e。somethingtobeginthemovementintheembryoandtodefinetheformitistoassume。Yetinsomeanimals，asbirds，thenatureofthefemaleunassistedcangeneratetoacertainextent，fortheydoformsomething，onlyitisincomplete；Imeantheso—calledwind—eggs。
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　　Forthesamereasonthedevelopmentoftheembryotakesplaceinthefemale；neitherthemalehimselfnorthefemaleemitssemenintothemale，butthefemalereceiveswithinherselfthesharecontributedbyboth，becauseinthefemaleisthematerialfromwhichismadetheresultingproduct。Notonlymustthemassofmaterialexisttherefromwhichtheembryoisformedinthefirstinstance，butfurthermaterialmustconstantlybeaddedthatitmayincreaseinsize。Thereforethebirthmusttakeplaceinthefemale。Forthecarpentermustkeepincloseconnexionwithhistimberandthepotterwithhisclay，andgenerallyallworkmanshipandtheultimatemovementimpartedtomattermustbeconnectedwiththematerialconcerned，as，forinstance，architectureisinthebuildingsitmakes。
　　Fromtheseconsiderationswemayalsogatherhowitisthatthemalecontributestogeneration。Themaledoesnotemitsemenatallinsomeanimals，andwherehedoesthisisnopartoftheresultingembryo；
　　justsonomaterialpartcomesfromthecarpentertothematerial，i。e。thewoodinwhichheworks，nordoesanypartofthecarpenter’sartexistwithinwhathemakes，buttheshapeandtheformareimpartedfromhimtothematerialbymeansofthemotionhesetsup。Itishishandsthatmovehistools，histoolsthatmovethematerial；itishisknowledgeofhisart，andhissoul，inwhichistheform，thatmoveshishandsoranyotherpartofhimwithamotionofsomedefinitekind，amotionvaryingwiththevaryingnatureoftheobjectmade。Inlikemanner，inthemaleofthoseanimalswhichemitsemenNatureusesthesemenasatoolandaspossessingmotioninactuality，justastoolsareusedintheproductsofanyart，forinthemliesinacertainsensethemotionoftheart。Such，then，isthewayinwhichthesemalescontributetogeneration。Butwhenthemaledoesnotemitsemen，butthefemaleinsertssomepartofherselfintothemale，thisisparalleltoacaseinwhichamanshouldcarrythematerialtotheworkman。ForbyreasonofweaknessinsuchmalesNatureisnotabletodoanythingbyanysecondarymeans，butthemovementsimpartedtothematerialarescarcelystrongenoughwhenNatureherselfwatchesoverthem。Thusheresheresemblesamodellerinclayratherthanacarpenter，forshedoesnottouchtheworksheisformingbymeansoftools，but，asitwere，withherownhands。
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　　Inallanimalswhichcanmoveabout，thesexesareseparated，oneindividualbeingmaleandonefemale，thoughbotharethesameinspecies，aswithmanandhorse。Butinplantsthesepowersaremingled，femalenotbeingseparatedfrommale。Whereforetheygenerateoutofthemselves，anddonotemitsemenbutproduceanembryo，whatiscalledtheseed。Empedoclesputsthiswellintheline：’andthusthetalltreesoviposit；firstolives……’Forastheeggisanembryo，acertainpartofitgivingrisetotheanimalandtherestbeingnutriment，soalsofromapartoftheseedspringsthegrowingplant，andtherestisnutrimentfortheshootandthefirstroot。
　　Inacertainsensethesamethinghappensalsointhoseanimalswhichhavethesexesseparate。Forwhenthereisneedforthemtogeneratethesexesarenolongerseparatedanymorethaninplants，theirnaturedesiringthattheyshallbecomeone；andthisisplaintoviewwhentheycopulateandareunited，thatoneanimalismadeoutofboth。
　　Itisthenatureofthosecreatureswhichdonotemitsementoremainunitedalongtimeuntilthemaleelementhasformedtheembryo，aswiththoseinsectswhichcopulate。Theotherssoremainonlyuntilthemalehasdischargedfromthepartsofhimselfintroducedsomethingwhichwillformtheembryoinalongertime，asamongthesanguinea。Fortheformerremainpairedsomepartofaday，whilethesemenformstheembryoinseveraldays。Andafteremittingthistheyceasetheirunion。
　　Andanimalsseemliterallytobelikedividedplants，asthoughoneshouldseparateanddividethem，whentheybearseed，intothemaleandfemaleexistinginthem。
　　InallthisNatureactslikeanintelligentworkman。Fortotheessenceofplantsbelongsnootherfunctionorbusinessthantheproductionofseed；since，then，thisisbroughtaboutbytheunionofmaleandfemale，Naturehasmixedtheseandsetthemtogetherinplants，sothatthesexesarenotdividedinthem。Plants，however，havebeeninvestigatedelsewhere。Butthefunctionoftheanimalisnotonlytogenerate（whichiscommontoalllivingthings），buttheyallofthemparticipatealsoinakindofknowledge，somemoreandsomeless，andsomeverylittleindeed。Fortheyhavesense—perception，andthisisakindofknowledge。（Ifweconsiderthevalueofthiswefindthatitisofgreatimportancecomparedwiththeclassoflifelessobjects，butoflittlecomparedwiththeuseoftheintellect。Foragainstthelatterthemereparticipationintouchandtasteseemstobepracticallynothing，butbesideabsoluteinsensibilityitseemsmostexcellent；foritwouldseematreasuretogaineventhiskindofknowledgeratherthantolieinastateofdeathandnon—existence。）Nowitisbysense—perceptionthatananimaldiffersfromthoseorganismswhichhaveonlylife。Butsince，ifitisalivinganimal，itmustalsolive；therefore，whenitisnecessaryforittoaccomplishthefunctionofthatwhichhaslife，itunitesandcopulates，becominglikeaplant，aswesaidbefore。
　　Testaceousanimals，beingintermediatebetweenanimalsandplants，performthefunctionofneitherclassasbelongingtoboth。Asplantstheyhavenosexes，andonedoesnotgenerateinanother；asanimalstheydonotbearfruitfromthemselveslikeplants；buttheyareformedandgeneratedfromaliquidandearthyconcretion。However，wemustspeaklaterofthegenerationoftheseanimals。
　　BookII
　　1
　　THATthemaleandthefemalearetheprinciplesofgenerationhasbeenpreviouslystated，asalsowhatistheirpowerandtheiressence。
　　Butwhyisitthatonethingbecomesandismale，anotherfemale？Itisthebusinessofourdiscussionasitproceedstotryandpointout（1）thatthesexesarisefromNecessityandthefirstefficientcause，（2）fromwhatsortofmaterialtheyareformed。That（3）theyexistbecauseitisbetterandonaccountofthefinalcause，takesusbacktoaprinciplestillfurtherremote。
　　Now（1）someexistingthingsareeternalanddivinewhilstothersadmitofbothexistenceandnon—existence。But（2）thatwhichisnobleanddivineisalways，invirtueofitsownnature，thecauseofthebetterinsuchthingsasadmitofbeingbetterorworse，andwhatisnoteternaldoesadmitofexistenceandnon—existence，andcanpartakeinthebetterandtheworse。And（3）soulisbetterthanbody，andliving，havingsoul，istherebybetterthanthelifelesswhichhasnone，andbeingisbetterthannotbeing，livingthannotliving。
　　These，then，arethereasonsofthegenerationofanimals。Forsinceitisimpossiblethatsuchaclassofthingsasanimalsshouldbeofaneternalnature，thereforethatwhichcomesintobeingiseternalintheonlywaypossible。Nowitisimpossibleforittobeeternalasanindividual（thoughofcoursetherealessenceofthingsisintheindividual）—wereitsuchitwouldbeeternal—butitispossibleforitasaspecies。Thisiswhythereisalwaysaclassofmenandanimalsandplants。Butsincethemaleandfemaleessencesarethefirstprinciplesofthese，theywillexistintheexistingindividualsforthesakeofgeneration。Again，asthefirstefficientormovingcause，towhichbelongthedefinitionandtheform，isbetterandmoredivineinitsnaturethanthematerialonwhichitworks，itisbetterthatthesuperiorprincipleshouldbeseparatedfromtheinferior。
　　Therefore，whereveritispossibleandsofarasitispossible，themaleisseparatedfromthefemale。Forthefirstprincipleofthemovement，orefficientcause，wherebythatwhichcomesintobeingismale，isbetterandmoredivinethanthematerialwherebyitisfemale。Themale，however，comestogetherandmingleswiththefemalefortheworkofgeneration，becausethisiscommontoboth。
　　Athinglives，then，invirtueofparticipatinginthemaleandfemaleprinciples，whereforeevenplantshavesomekindoflife；buttheclassofanimalsexistsinvirtueofsense—perception。Thesexesaredividedinnearlyallofthesethatcanmoveabout，forthereasonsalreadystated，andsomeofthem，assaidbefore，emitsemenincopulation，othersnot。Thereasonofthisisthatthehigheranimalsaremoreindependentintheirnature，sothattheyhavegreatersize，andthiscannotexistwithoutvitalheat；forthegreaterbodyrequiresmoreforcetomoveit，andheatisamotiveforce。Therefore，takingageneralview，wemaysaythatsanguineaareofgreatersizethanbloodlessanimals，andthosewhichmoveaboutthanthosewhichremainfixed。Andthesearejusttheanimalswhichemitsemenonaccountoftheirheatandsize。
　　Somuchforthecauseoftheexistenceofthetwosexes。Someanimalsbringtoperfectionandproduceintotheworldacreaturelikethemselves，asallthosewhichbringtheiryoungintotheworldalive；
　　othersproducesomethingundevelopedwhichhasnotyetacquireditsownform；inthislatterdivisionthesanguinealayeggs，thebloodlessanimalseitherlayaneggorgivebirthtoascolex。Thedifferencebetweeneggandscolexisthis：aneggisthatfromapartofwhichtheyoungcomesintobeing，therestbeingnutrimentforit；butthewholeofascolexisdevelopedintothewholeoftheyounganimal。Ofthevivipara，whichbringintotheworldananimallikethemselves，someareinternallyviviparous（asmen，horses，cattle，andofmarineanimalsdolphinsandtheothercetacea）；othersfirstlayeggswithinthemselves，andonlyafterthisareexternallyviviparous（asthecartilaginousfishes）。Amongtheoviparasomeproducetheegginaperfectcondition（asbirdsandalloviparousquadrupedsandfootlessanimals，e。g。lizardsandtortoisesandmostsnakes；fortheeggsofallthesedonotincreasewhenoncelaid）。
　　Theeggsofothersareimperfect；sucharethoseoffishes，crustaceans，andcephalopods，fortheireggsincreaseafterbeingproduced。
　　Alltheviviparaaresanguineous，andthesanguineaareeitherviviparousoroviparous，exceptthosewhicharealtogetherinfertile。Amongbloodlessanimalstheinsectsproduceascolex，alikethosethataregeneratedbycopulationandthosethatcopulatethemselvesthoughnotsogenerated。Fortherearesomeinsectsofthissort，whichthoughtheycomeintobeingbyspontaneousgenerationareyetmaleandfemale；fromtheirunionsomethingisproduced，onlyitisimperfect；thereasonofthishasbeenpreviouslystated。
　　Theseclassesadmitofmuchcross—division。Notallbipedsareviviparous（forbirdsareoviparous），noraretheyalloviparous（formanisviviparous），norareallquadrupedsoviparous（forhorses，cattle，andcountlessothersareviviparous），noraretheyallviviparous（forlizards，crocodiles，andmanyotherslayeggs）。
　　Nordoesthepresenceorabsenceoffeetmakethedifferencebetweenthem，fornotonlyaresomefootlessanimalsviviparous，asvipersandthecartilaginousfishes，whileothersareoviparous，astheotherfishesandserpents，butalsoamongthosewhichhavefeetmanyareoviparousandmanyviviparous，asthequadrupedsabovementioned。Andsomewhichhavefeet，asman，andsomewhichhavenot，asthewhaleanddolphin，areinternallyviviparous。Bythischaracterthenitisnotpossibletodividethem，norisanyofthelocomotiveorgansthecauseofthisdifference，butitisthoseanimalswhicharemoreperfectintheirnatureandparticipateinapurerelementwhichareviviparous，fornothingisinternallyviviparousunlessitreceiveandbreatheoutair。Butthemoreperfectarethosewhicharehotterintheirnatureandhavemoremoistureandarenotearthyintheircomposition。Andthemeasureofnaturalheatisthelungwhenithasbloodinit，forgenerallythoseanimalswhichhavealungarehotterthanthosewhichhavenot，andintheformerclassagainthosewhoselungisnotspongynorsolidnorcontainingonlyalittleblood，butsoftandfullofblood。Andastheanimalisperfectbuttheeggandthescolexareimperfect，sotheperfectisnaturallyproducedfromthemoreperfect。Ifanimalsarehotterasshownbytheirpossessingalungbutdrierintheirnature，orarecolderbuthavemoremoisture，thentheyeitherlayaperfecteggorareviviparousafterlayinganeggwithinthemselves。
　　Forbirdsandscalyreptilesbecauseoftheirheatproduceaperfectegg，butbecauseoftheirdrynessitisonlyanegg；thecartilaginousfisheshavelessheatthanthesebutmoremoisture，sothattheyareintermediate，fortheyarebothoviparousandviviparouswithinthemselves，theformerbecausetheyarecold，thelatterbecauseoftheirmoisture；formoistureisvivifying，whereasdrynessisfurthestremovedfromwhathaslife。Sincetheyhaveneitherfeathersnorscalessuchaseitherreptilesorotherfisheshave，allwhicharesignsratherofadryandearthynature，theeggtheyproduceissoft；
　　fortheearthymatterdoesnotcometothesurfaceintheireggsanymorethaninthemselves。Thisiswhytheylayeggsinthemselves，foriftheeggwerelaidexternallyitwouldbedestroyed，havingnoprotection。
　　Animalsthatarecoldandratherdrythanmoistalsolayeggs，buttheeggisimperfect；atthesametime，becausetheyareofanearthynatureandtheeggtheyproduceisimperfect，thereforeithasahardintegumentthatitmaybepreservedbytheprotectionoftheshell—likecovering。Hencefishes，becausetheyarescaly，andcrustacea，becausetheyareofanearthynature，layeggswithahardintegument。
　　Thecephalopods，havingthemselvesbodiesofastickynature，preserveinthesamewaytheimperfecteggstheylay，fortheydepositaquantityofstickymaterialabouttheembryo。Allinsectsproduceascolex。Nowalltheinsectsarebloodless，whereforeallcreaturesthatproduceascolexfromthemselvesareso。Butwecannotsaysimplythatallbloodlessanimalsproduceascolex，fortheclassesoverlaponeanother，（1）theinsects，（2）theanimalsthatproduceascolex，（3）thosethatlaytheireggimperfect，asthescalyfishes，thecrustacea，andthecephalopoda。Isaythattheseformagradation，fortheeggsoftheselatterresembleascolex，inthattheyincreaseafteroviposition，andthescolexofinsectsagainasitdevelopsresemblesanegg；howsoweshallexplainlater。
　　WemustobservehowrightlyNatureordersgenerationinregulargradation。Themoreperfectandhotteranimalsproducetheiryoungperfectinrespectofquality（inrespectofquantitythisissowithnoanimal，fortheyoungalwaysincreaseinsizeafterbirth），andthesegeneratelivinganimalswithinthemselvesfromthefirst。Thesecondclassdonotgenerateperfectanimalswithinthemselvesfromthefirst（fortheyareonlyviviparousafterfirstlayingeggs），butstilltheyareexternallyviviparous。Thethirdclassdonotproduceaperfectanimal，butanegg，andthiseggisperfect。Thosewhosenatureisstillcolderthantheseproduceanegg，butanimperfectone，whichisperfectedoutsidethebody，astheclassofscalyfishes，thecrustacea，andthecephalopods。Thefifthandcoldestclassdoesnotevenlayaneggfromitself；butsofarastheyoungeverattaintothisconditionatall，itisoutsidethebodyoftheparent，ashasbeensaidalready。Forinsectsproduceascolexfirst；thescolexafterdevelopingbecomesegg—like（fortheso—calledchrysalisorpupaisequivalenttoanegg）；thenfromthisitisthataperfectanimalcomesintobeing，reachingtheendofitsdevelopmentinthesecondchange。
　　Someanimalsthen，assaidbefore，donotcomeintobeingfromsemen，butallthesanguineadosowhicharegeneratedbycopulation，themaleemittingsemenintothefemalewhenthishasenteredintohertheyoungareformedandassumetheirpeculiarcharacter，somewithintheanimalsthemselveswhentheyareviviparous，othersineggs。
　　Thereisaconsiderabledifficultyinunderstandinghowtheplantisformedoutoftheseedoranyanimaloutofthesemen。Everythingthatcomesintobeingorismademust（1）bemadeoutofsomething，（2）
　　bemadebytheagencyofsomething，and（3）mustbecomesomething。Nowthatoutofwhichitismadeisthematerial；thissomeanimalshaveinitsfirstformwithinthemselves，takingitfromthefemaleparent，asallthosewhicharenotbornalivebutproducedasascolexoranegg；othersreceiveitfromthemotherforalongtimebysucking，astheyoungofallthosewhicharenotonlyexternallybutalsointernallyviviparous。Such，then，isthematerialoutofwhichthingscomeintobeing，butwenowareinquiringnotoutofwhatthepartsofananimalaremade，butbywhatagency。Eitheritissomethingexternalwhichmakesthem，orelsesomethingexistingintheseminalfluidandthesemen；andthismusteitherbesoulorapartofsoul，orsomethingcontainingsoul。
　　Nowitwouldappearirrationaltosupposethatanyofeithertheinternalorgansortheotherpartsismadebysomethingexternal，sinceonethingcannotsetupamotioninanotherwithouttouchingit，norcanathingbeaffectedinanywaybyanotherifitdoesnotsetupamotioninit。Somethingthenofthesortwerequireexistsintheembryoitself，beingeitherapartofitorseparatefromit。Tosupposethatitshouldbesomethingelseseparatefromitisirrational。Foraftertheanimalhasbeenproduceddoesthissomethingperishordoesitremaininit？Butnothingofthekindappearstobeinit，nothingwhichisnotapartofthewholeplantoranimal。
　　Yet，ontheotherhand，itisabsurdtosaythatitperishesaftermakingeitherallthepartsoronlysomeofthem。Ifitmakessomeofthepartsandthenperishes，whatistomaketherestofthem？
　　Supposethissomethingmakestheheartandthenperishes，andtheheartmakesanotherorgan，bythesameargumenteitherallthepartsmustperishorallmustremain。Thereforeitispreservedanddoesnotperish。Thereforeitisapartoftheembryoitselfwhichexistsinthesemenfromthebeginning；andifindeedthereisnopartofthesoulwhichdoesnotexistinsomepartofthebody，itwouldalsobeapartcontainingsoulinitfromthebeginning。
　　How，then，doesitmaketheotherparts？Eitheralltheparts，asheart，lung，liver，eye，andalltherest，comeintobeingtogetherorinsuccession，asissaidintheverseascribedtoOrpheus，fortherehesaysthatananimalcomesintobeinginthesamewayastheknittingofanet。Thattheformerisnotthefactisplaineventothesenses，forsomeofthepartsareclearlyvisibleasalreadyexistingintheembryowhileothersarenot；thatitisnotbecauseoftheirbeingtoosmallthattheyarenotvisibleisclear，forthelungisofgreatersizethantheheart，andyetappearslaterthantheheartintheoriginaldevelopment。Since，then，oneisearlierandanotherlater，doestheonemaketheother，anddoesthelaterpartexistonaccountofthepartwhichisnexttoit，orratherdoestheonecomeintobeingonlyaftertheother？Imean，forinstance，thatitisnotthefactthattheheart，havingcomeintobeingfirst，thenmakestheliver，andtheliveragainanotherorgan，butthattheliveronlycomesintobeingaftertheheart，andnotbytheagencyoftheheart，asamanbecomesamanafterbeingaboy，notbyhisagency。Anexplanationofthisisthat，inalltheproductionsofNatureorofart，whatalreadyexistspotentiallyisbroughtintobeingonlybywhatexistsactually；thereforeifoneorganformedanothertheformandthecharacterofthelaterorganwouldhavetoexistintheearlier，e。g。theformoftheliverintheheart。Andotherwisealsothetheoryisstrangeandfictitious。
　　Yetagain，ifthewholeanimalorplantisformedfromsemenorseed，itisimpossiblethatanypartofitshouldexistreadymadeinthesemenorseed，whetherthatpartbeabletomaketheotherpartsorno。Foritisplainthat，ifitexistsinitfromthefirst，itwasmadebythatwhichmadethesemen。Butsemenmustbemadefirst，andthatisthefunctionofthegeneratingparent。So，then，itisnotpossiblethatanypartshouldexistinit，andthereforeithasnotwithinitselfthatwhichmakestheparts。
　　Butneithercanthisagentbeexternal，andyetitmustneedsbeoneorotherofthetwo。Wemusttry，then，tosolvethisdifficulty，forperhapssomeoneofthestatementsmadecannotbemadewithoutqualification，e。g。thestatementthatthepartscannotbemadebywhatisexternaltothesemen。Forifinacertainsensetheycannot，yetinanothersensetheycan。（Nowitmakesnodifferencewhetherwesay’thesemen’or’thatfromwhichthesemencomes’，insofarasthesemenhasinitselfthemovementinitiatedbytheother。）
　　Itispossible，then，thatAshouldmoveB，andBmoveC；that，infact，thecaseshouldbethesameaswiththeautomaticmachinesshownascuriosities。Forthepartsofsuchmachineswhileatresthaveasortofpotentialityofmotioninthem，andwhenanyexternalforceputsthefirstoftheminmotion，immediatelythenextismovedinactuality。As，then，intheseautomaticmachinestheexternalforcemovesthepartsinacertainsense（notbytouchinganypartatthemoment，butbyhavingtouchedonepreviously），inlikemanneralsothatfromwhichthesemencomes，orinotherwordsthatwhichmadethesemen，setsupthemovementintheembryoandmakesthepartsofitbyhavingfirsttouchedsomethingthoughnotcontinuingtotouchit。Inawayitistheinnatemotionthatdoesthis，astheactofbuildingbuildsthehouse。Plainly，then，whilethereissomethingwhichmakestheparts，thisdoesnotexistasadefiniteobject，nordoesitexistinthesemenatthefirstasacompletepart。
　　Buthowiseachpartformed？Wemustanswerthisbystartinginthefirstinstancefromtheprinciplethat，inallproductsofNatureorart，athingismadebysomethingactuallyexistingoutofthatwhichispotentiallysuchasthefinishedproduct。Nowthesemenisofsuchanature，andhasinitsuchaprincipleofmotion，thatwhenthemotionisceasingeachofthepartscomesintobeing，andthatasaparthavinglifeorsoul。Forthereisnosuchthingasfaceorfleshwithoutlifeorsoulinit；itisonlyequivocallythattheywillbecalledfaceorfleshifthelifehasgoneoutofthem，justasiftheyhadbeenmadeofstoneorwood。Andthehomogeneouspartsandtheorganiccomeintobeingtogether。Andjustasweshouldnotsaythatanaxeorotherinstrumentororganwasmadebythefirealone，soneithershallwesaythatfootorhandweremadebyheatalone。Thesameappliesalsotoflesh，forthistoohasafunction。While，then，wemayallowthathardnessandsoftness，stickinessandbrittleness，andwhateverotherqualitiesarefoundinthepartsthathavelifeandsoul，maybecausedbymereheatandcold，yet，whenwecometotheprincipleinvirtueofwhichfleshisfleshandboneisbone，thatisnolongerso；whatmakesthemisthemovementsetupbythemaleparent，whoisinactualitywhatthatoutofwhichtheoffspringismadeisinpotentiality。Thisiswhatwefindintheproductsofart；heatandcoldmaymaketheironsoftandhard，butwhatmakesaswordisthemovementofthetoolsemployed，thismovementcontainingtheprincipleoftheart。Fortheartisthestarting—pointandformoftheproduct；onlyitexistsinsomethingelse，whereasthemovementofNatureexistsintheproductitself，issuingfromanothernaturewhichhastheforminactuality。
　　Hasthesemensoul，ornot？Thesameargumentapplieshereasinthequestionconcerningtheparts。Asnopart，ifitparticipatenotinsoul，willbeapartexceptinanequivocalsense（astheeyeofadeadmanisstillcalledan’eye’），sonosoulwillexistinanythingexceptthatofwhichitissoul；itisplainthereforethatsemenbothhassoul，andissoul，potentially。
　　Butathingexistingpotentiallymaybenearerorfurtherfromitsrealizationinactuality，ase。g。amathematicianwhenasleepisfurtherfromhisrealizationinactualityasengagedinmathematicsthanwhenheisawake，andwhenawakeagainbutnotstudyingmathematicsheisfurtherremovedthanwhenheissostudying。
　　Accordinglyitisnotanypartthatisthecauseofthesoul’scomingintobeing，butitisthefirstmovingcausefromoutside。
　　（Fornothinggeneratesitself，thoughwhenithascomeintobeingitthenceforwardincreasesitself。）Henceitisthatonlyonepartcomesintobeingfirstandnotallofthemtogether。Butthatmustfirstcomeintobeingwhichhasaprincipleofincrease（forthisnutritivepowerexistsinallalike，whetheranimalsorplants，andthisisthesameasthepowerthatenablesananimalorplanttogenerateanotherlikeitself，thatbeingthefunctionofthemallifnaturallyperfect）。Andthisisnecessaryforthereasonthatwheneveralivingthingisproduceditmustgrow。Itisproduced，then，bysomethingelseofthesamename，ase。g。manisproducedbyman，butitisincreasedbymeansofitself。Thereis，then，somethingwhichincreasesit。Ifthisisasinglepart，thismustcomeintobeingfirst。Thereforeiftheheartisfirstmadeinsomeanimals，andwhatisanalogoustotheheartintheotherswhichhavenoheart，itisfromthisoritsanaloguethatthefirstprincipleofmovementwouldarise。
　　Wehavethusdiscussedthedifficultiespreviouslyraisedonthequestionwhatistheefficientcauseofgenerationineachcase，asthefirstmovingandformativepower。
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　　Thenextquestiontobemootedconcernsthenatureofsemen。Forwhereaswhenitissuesfromtheanimalitisthickandwhite，yetoncoolingitbecomesliquidaswater，anditscolouristhatofwater。
　　Thiswouldappearstrange，forwaterisnotthickenedbyheat；yetsemenisthickwhenitissuesfromwithintheanimal’sbodywhichishot，andbecomesliquidoncooling。Again，wateryfluidsfreeze，butsemen，ifexposedinfroststotheopenair，doesnotfreezebutliquefies，asifitwasthickenedbytheoppositeofcold。Yetitisunreasonable，again，tosupposethatitisthickenedbyheat。Foritisonlysubstanceshavingapredominanceofearthintheircompositionthatcoagulateandthickenonboiling，e。g。milk。Itoughtthentosolidifyoncooling，butasamatteroffactitdoesnotbecomesolidinanypartbutthewholeofitgoeslikewater。
　　Thisthenisthedifficulty。Ifitiswater，waterevidentlydoesnotthickenthroughheat，whereasthesemenisthickandbothitandthebodywhenceitissuesarehot。Ifitismadeofearthoramixtureofearthandwater，itoughtnottoliquefyentirelyandturntowater。
　　Perhaps，however，wehavenotdiscriminatedallthepossibilities。
　　Itisnotonlytheliquidscomposedofwaterandearthymatterthatthicken，butalsothosecomposedofwaterandair；foam，forinstance，becomesthickerandwhite，andthesmallerandlessvisiblethebubblesinit，thewhiterandfirmerdoesthemassappear。Thesamethinghappensalsowithoil；onmixingwithairitthickens，whereforethatwhichiswhiteningbecomesthicker，thewaterypartinitbeingseparatedoffbytheheatandturningtoair。Andifoxideofleadismixedwithwaterorevenwithoil，themassincreasesgreatlyandchangesfromliquidanddarktofirmandwhite，thereasonbeingthatairismixedinwithitwhichincreasesthemassandmakesthewhiteshinethrough，asinfoamandsnow（forsnowisfoam）。Andwateritselfonminglingwithoilbecomesthickandwhite，becauseairisentangledinitbytheactofpoundingthemtogether，andoilitselfhasmuchairinit（forshininessisapropertyofair，notofearthorwater）。Thistooiswhyitfloatsonthesurfaceofthewater，fortheaircontainedinitasinavesselbearsitupandmakesitfloat，beingthecauseofitslightness。Sotoooilisthickenedwithoutfreezingincoldweatherandfrosts；itdoesnotfreezebecauseofitsheat（fortheairishotandwillnotfreeze），butbecausetheairisforcedtogetherandcompressed，as……，bythecold，theoilbecomesthicker。Thesearethereasonswhysemenisfirmandwhitewhenitissuesfromwithintheanimal；ithasaquantityofhotairinitbecauseoftheinternalheat；afterwards，whentheheathasevaporatedandtheairhascooled，itturnsliquidanddark；forthewater，andanysmallquantityofearthymattertheremaybe，remaininsemenasitdries，astheydoinphlegm。
　　Semen，then，isacompoundofspirit（pneuma）andwater，andtheformerishotair（aerh）；hencesemenisliquidinitsnaturebecauseitismadeofwater。WhatCtesiastheCnidianhasassertedofthesemenofelephantsismanifestlyuntrue；hesaysthatithardenssomuchindryingthatitbecomeslikeamber。Butthisdoesnothappen，thoughitistruethatonesemenmustbemoreearthythananother，andespeciallysowithanimalsthathavemuchearthymatterinthembecauseofthebulkoftheirbodies。Anditisthickandwhitebecauseitismixedwithspirit，foritisalsoaninvariablerulethatitiswhite，andHerodotusdoesnotreportthetruthwhenhesaysthatthesemenoftheAethiopiansisblack，asifeverythingmustneedsbeblackinthosewhohaveablackskin，andthattoowhenhesawtheirteethwerewhite。Thereasonofthewhitenessofsemenisthatitisafoam，andfoamiswhite，especiallythatwhichiscomposedofthesmallestparts，smallinthesensethateachbubbleisinvisible，whichiswhathappenswhenwaterandoilaremixedandshakentogether，assaidbefore。（Eventheancientsseemtohavenoticedthatsemenisofthenatureoffoam；atleastitwasfromthistheynamedthegoddesswhopresidesoverunion。）
　　Thisthenistheexplanationoftheproblemproposed，anditisplaintoothatthisiswhysemendoesnotfreeze；forairwillnotfreeze。
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　　Thenextquestiontoraiseandtoansweristhis。If，inthecaseofthoseanimalswhichemitsemenintothefemale，thatwhichentersmakesnopartoftheresultingembryo，whereisthematerialpartofitdivertedif（aswehaveseen）itactsbymeansofthepowerresidinginit？Itisnotonlynecessarytodecidewhetherwhatisforminginthefemalereceivesanythingmaterial，ornot，fromthatwhichhasenteredher，butalsoconcerningthesoulinvirtueofwhichananimalissocalled（andthisisinvirtueofthesensitivepartofthesoul）—doesthisexistoriginallyinthesemenandintheunfertilizedembryoornot，andifitdoeswhencedoesitcome？Fornobodywouldputdowntheunfertilizedembryoassoullessorineverysensebereftoflife（sinceboththesemenandtheembryoofananimalhaveeverybitasmuchlifeasaplant），anditisproductiveuptoacertainpoint。Thatthentheypossessthenutritivesoulisplain（andplainisitfromthediscussionselsewhereaboutsoulwhythissoulmustbeacquiredfirst）。Astheydeveloptheyalsoacquirethesensitivesoulinvirtueofwhichananimalisananimal。Fore。g。ananimaldoesnotbecomeatthesametimeananimalandamanorahorseoranyotherparticularanimal。Fortheendisdevelopedlast，andthepeculiarcharacterofthespeciesistheendofthegenerationineachindividual。Hencearisesaquestionofthegreatestdifficulty，whichwemuststrivetosolvetothebestofourabilityandasfaraspossible。Whenandhowandwhenceisashareinreasonacquiredbythoseanimalsthatparticipateinthisprinciple？Itisplainthatthesemenandtheunfertilizedembryo，whilestillseparatefromeachother，mustbeassumedtohavethenutritivesoulpotentially，butnotactually，exceptthat（likethoseunfertilizedembryosthatareseparatedfromthemother）
　　itabsorbsnourishmentandperformsthefunctionofthenutritivesoul。Foratfirstallsuchembryosseemtolivethelifeofaplant。Anditisclearthatwemustbeguidedbythisinspeakingofthesensitiveandtherationalsoul。Forallthreekindsofsoul，notonlythenutritive，mustbepossessedpotentiallybeforetheyarepossessedinactuality。Anditisnecessaryeither（1）thattheyshouldallcomeintobeingintheembryowithoutexistingpreviouslyoutsideit，or（2）thattheyshouldallexistpreviously，or（3），thatsomeshouldsoexistandothersnot。Again，itisnecessarythattheyshouldeither（1）comeintobeinginthematerialsuppliedbythefemalewithoutenteringwiththesemenofthemale，or（2）comefromthemaleandbeimpartedtothematerialinthefemale。Ifthelatter，theneitherallofthem，ornone，orsomemustcomeintobeinginthemalefromoutside。
　　Nowthatitisimpossibleforthemalltopreexistisclearfromthisconsideration。Plainlythoseprincipleswhoseactivityisbodilycannotexistwithoutabody，e。g。walkingcannotexistwithoutfeet。Forthesamereasonalsotheycannotenterfromoutside。
　　Forneitherisitpossibleforthemtoenterbythemselves，beinginseparablefromabody，noryetinabody，forthesemenisonlyasecretionofthenutrimentinprocessofchange。Itremains，then，forthereasonalonesotoenterandalonetobedivine，fornobodilyactivityhasanyconnexionwiththeactivityofreason。
　　Nowitistruethatthefacultyofallkindsofsoulseemstohaveaconnexionwithamatterdifferentfromandmoredivinethantheso—calledelements；butasonesouldiffersfromanotherinhonouranddishonour，sodiffersalsothenatureofthecorrespondingmatter。Allhaveintheirsementhatwhichcausesittobeproductive；Imeanwhatiscalledvitalheat。Thisisnotfirenoranysuchforce，butitisthespiritusincludedinthesemenandthefoam—like，andthenaturalprincipleinthespiritus，beinganalogoustotheelementofthestars。Hence，whereasfiregeneratesnoanimalandwedonotfindanylivingthingformingineithersolidsorliquidsundertheinfluenceoffire，theheatofthesunandthatofanimalsdoesgeneratethem。Notonlyisthistrueoftheheatthatworksthroughthesemen，butwhateverotherresiduumoftheanimalnaturetheremaybe，thisalsohasstillavitalprincipleinit。Fromsuchconsiderationsitisclearthattheheatinanimalsneitherisfirenorderivesitsoriginfromfire。
　　Letusreturntothematerialofthesemen，inandwithwhichcomesawayfromthemalethespiritusconveyingtheprincipleofsoul。
　　Ofthisprincipletherearetwokinds；theoneisnotconnectedwithmatter，andbelongstothoseanimalsinwhichisincludedsomethingdivine（towit，whatiscalledthereason），whiletheotherisinseparablefrommatter。Thismaterialofthesemendissolvesandevaporatesbecauseithasaliquidandwaterynature。Thereforeweoughtnottoexpectitalwaystocomeoutagainfromthefemaleortoformanypartoftheembryothathastakenshapefromit；thecaseresemblesthatofthefig—juicewhichcurdlesmilk，forthistoochangeswithoutbecominganypartofthecurdlingmasses。