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　　WEhavenowdiscussedtheotherpartsofanimals，bothgenerallyandwithreferencetothepeculiaritiesofeachkind，explaininghoweachpartexistsonaccountofsuchacause，andImeanbythisthefinalcause。
　　Therearefourcausesunderlyingeverything：first，thefinalcause，thatforthesakeofwhichathingexists；secondly，theformalcause，thedefinitionofitsessence（andthesetwowemayregardprettymuchasoneandthesame）；thirdly，thematerial；andfourthly，themovingprincipleorefficientcause。
　　Wehavethenalreadydiscussedtheotherthreecauses，forthedefinitionandthefinalcausearethesame，andthematerialofanimalsistheirpartsofthewholeanimalthenon—homogeneousparts，oftheseagainthehomogeneous，andoftheselasttheso—calledelementsofallmatter。Itremainstospeakofthosepartswhichcontributetothegenerationofanimalsandofwhichnothingdefinitehasyetbeensaid，andtoexplainwhatisthemovingorefficientcause。Toinquireintothislastandtoinquireintothegenerationofeachanimalisinawaythesamething；and，therefore，myplanhasunitedthemtogether，arrangingthediscussionofthesepartslast，andthebeginningofthequestionofgenerationnexttothem。
　　Nowsomeanimalscomeintobeingfromtheunionofmaleandfemale，i。e。allthosekindsofanimalwhichpossessthetwosexes。
　　Thisisnotthecasewithallofthem；thoughinthesanguineawithfewexceptionsthecreature，whenitsgrowthiscomplete，iseithermaleorfemale，andthoughsomebloodlessanimalshavesexessothattheygenerateoffspringofthesamekind，yetotherbloodlessanimalsgenerateindeed，butnotoffspringofthesamekind；suchareallthatcomeintobeingnotfromaunionofthesexes，butfromdecayingearthandexcrements。Tospeakgenerally，ifwetakeallanimalswhichchangetheirlocality，somebyswimming，othersbyflying，othersbywalking，wefindinthesethetwosexes，notonlyinthesanguineabutalsoinsomeofthebloodlessanimals；andthisappliesinthecaseofthelattersometimestothewholeclass，asthecephalopodaandcrustacea，butintheclassofinsectsonlytothemajority。Ofthese，allwhichareproducedbyunionofanimalsofthesamekindgeneratealsoaftertheirkind，butallwhicharenotproducedbyanimals，butfromdecayingmatter，generateindeed，butproduceanotherkind，andtheoffspringisneithermalenorfemale；
　　sucharesomeoftheinsects。Thisiswhatmighthavebeenexpected，forifthoseanimalswhicharenotproducedbyparentshadthemselvesunitedandproducedothers，thentheiroffspringmusthavebeeneitherlikeorunliketothemselves。Iflike，thentheirparentsoughttohavecomeintobeinginthesameway；thisisonlyareasonablepostulatetomake，foritisplainlythecasewithotheranimals。Ifunlike，andyetabletocopulate，thentherewouldhavecomeintobeingagainfromthemanotherkindofcreatureandagainanotherfromthese，andthiswouldhavegoneontoinfinity。ButNaturefliesfromtheinfinite，fortheinfiniteisunendingorimperfect，andNatureeverseeksanend。
　　Butallthosecreatureswhichdonotmove，asthetestaceaandanimalsthatlivebyclingingtosomethingelse，inasmuchastheirnatureresemblesthatofplants，havenosexanymorethanplantshave，butasappliedtothemthewordisonlyusedinvirtueofasimilarityandanalogy。Forthereisaslightdistinctionofthissort，sinceeveninplantswefindinthesamekindsometreeswhichbearfruitandotherswhich，whilebearingnonethemselves，yetcontributetotheripeningofthefruitsofthosewhichdo，asinthecaseofthefig—treeandcaprifig。
　　Thesameholdsgoodalsoinplants，somecomingintobeingfromseedandothers，asitwere，bythespontaneousactionofNature，arisingeitherfromdecompositionoftheearthorofsomepartsinotherplants，forsomearenotformedbythemselvesseparatelybutareproduceduponothertrees，asthemistletoe。Plants，however，mustbeinvestigatedseparately。
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　　Ofthegenerationofanimalswemustspeakasvariousquestionsariseinorderinthecaseofeach，andwemustconnectouraccountwithwhathasbeensaid。For，aswesaidabove，themaleandfemaleprinciplesmaybeputdownfirstandforemostasoriginsofgeneration，theformerascontainingtheefficientcauseofgeneration，thelatterthematerialofit。Themostconclusiveproofofthisisdrawnfromconsideringhowandwhencecomesthesemen；
　　forthereisnodoubtthatitisoutofthisthatthosecreaturesareformedwhichareproducedintheordinarycourseofNature；butwemustobservecarefullythewayinwhichthissemenactuallycomesintobeingfromthemaleandfemale。Foritisjustbecausethesemenissecretedfromthetwosexes，thesecretiontakingplaceinthemandfromthem，thattheyarefirstprinciplesofgeneration。Forbyamaleanimalwemeanthatwhichgeneratesinanother，andbyafemalethatwhichgeneratesinitself；whereforemenapplythesetermstothemacrocosmalso，namingEarthmotherasbeingfemale，butaddressingHeavenandtheSunandotherlikeentitiesasfathers，ascausinggeneration。
　　Maleandfemaledifferintheiressencebyeachhavingaseparateabilityorfaculty，andanatomicallybycertainparts；essentiallythemaleisthatwhichisabletogenerateinanother，assaidabove；
　　thefemaleisthatwhichisabletogenerateinitselfandoutofwhichcomesintobeingtheoffspringpreviouslyexistingintheparent。Andsincetheyaredifferentiatedbyanabilityorfacultyandbytheirfunction，andsinceinstrumentsororgansareneededforallfunctioning，andsincethebodilypartsaretheinstrumentsororganstoservethefaculties，itfollowsthatcertainpartsmustexistforunionofparentsandproductionofoffspring。Andthesemustdifferfromeachother，sothatconsequentlythemalewilldifferfromthefemale。（Foreventhoughwespeakoftheanimalasawholeasmaleorfemale，yetreallyitisnotmaleorfemaleinvirtueofthewholeofitself，butonlyinvirtueofacertainfacultyandacertainpart—justaswiththepartusedforsightorlocomotion—whichpartisalsoplaintosense—perception。）
　　Nowasamatteroffactsuchpartsareinthefemaletheso—calleduterus，inthemalethetestesandthepenis，inallthesanguinea；
　　forsomeofthemhavetestesandothersthecorrespondingpassages。
　　Therearecorrespondingdifferencesofmaleandfemaleinallthebloodlessanimalsalsowhichhavethisdivisionintooppositesexes。
　　Butifinthesanguineaitisthepartsconcernedincopulationthatdifferprimarilyintheirforms，wemustobservethatasmallchangeinafirstprincipleisoftenattendedbychangesinotherthingsdependingonit。Thisisplaininthecaseofcastratedanimals，for，thoughonlythegenerativepartisdisabled，yetprettywellthewholeformoftheanimalchangesinconsequencesomuchthatitseemstobefemaleornotfarshortofit，andthusitisclearthanananimalisnotmaleorfemaleinvirtueofanisolatedpartoranisolatedfaculty。Clearly，then，thedistinctionofsexisafirstprinciple；atanyrate，whenthatwhichdistinguishesmaleandfemalesufferschange，manyotherchangesaccompanyit，aswouldbethecaseifafirstprincipleischanged。
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　　Thesanguineaarenotallalikeasregardstestesanduterus。Takingtheformerfirst，wefindthatsomeofthemhavenottestesatall，astheclassesoffishandofserpents，butonlytwospermaticducts。
　　Othershavetestesindeed，butinternallybytheloinintheregionofthekidneys，andfromeachoftheseaduct，asinthecaseofthoseanimalswhichhavenotestesatall，theseductsunitealsoaswiththoseanimals；thisapplies（amonganimalsbreathingairandhavingalung）toallbirdsandoviparousquadrupeds。Forallthesehavetheirtestesinternalneartheloin，andtwoductsfromtheseinthesamewayasserpents；Imeanthelizardsandtortoisesandallthescalyreptiles。Butalltheviviparahavetheirtestesinfront；someoftheminsideattheendoftheabdomen，asthedolphin，notwithductsbutwithapenisprojectingexternallyfromthem；othersoutside，eitherpendentasinmanortowardsthefundamentasinswine。TheyhavebeendiscriminatedmoreaccuratelyintheEnquiriesaboutAnimals。
　　Theuterusisalwaysdouble，justasthetestesarealwaystwointhemale。Itissituatedeithernearthepudendum（asinwomen，andallthoseanimalswhichbringforthalivenotonlyexternallybutalsointernally，andallfishthatlayeggsexternally）oruptowardsthehypozoma（asinallbirdsandinviviparousfishes）。Theuterusisalsodoubleinthecrustaceaandthecephalopoda，forthemembraneswhichincludetheirso—calledeggsareofthenatureofauterus。Itisparticularlyhardtodistinguishinthecaseofthepoulps，sothatitseemstobesingle，butthereasonofthisisthatthebulkofthebodyiseverywheresimilar。
　　Itisdoublealsointhelargerinsects；inthesmallerthequestionisuncertainowingtothesmallsizeofthebody。
　　Suchisthedescriptionoftheaforesaidpartsofanimals。
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　　Withregardtothedifferenceofthespermaticorgansinmales，ifwearetoinvestigatethecausesoftheirexistence，wemustfirstgraspthefinalcauseofthetestes。NowifNaturemakeseverythingeitherbecauseitisnecessaryorbecauseitisbetterso，thispartalsomustbeforoneofthesetworeasons。Butthatitisnotnecessaryforgenerationisplain；elsehaditbeenpossessedbyallcreaturesthatgenerate，butasitisneitherserpentshavetestesnorhavefish；fortheyhavebeenseenunitingandwiththeirductsfullofmilt。Itremainsthenthatitmustbebecauseitissomehowbetterso。Nowitistruethatthebusinessofmostanimalsis，youmaysay，nothingelsethantoproduceyoung，asthebusinessofaplantistoproduceseedandfruit。Butstillas，inthecaseofnutriment，animalswithstraightintestinesaremoreviolentintheirdesireforfood，sothosewhichhavenottestesbutonlyducts，orwhichhavethemindeedbutinternally，areallquickerinaccomplishingcopulation。Butthosewhicharetobemoretemperateintheonecasehavenotstraightintestines，andintheotherhavetheirductstwistedtopreventtheirdesirebeingtooviolentandhasty。Itisforthisthatthetestesarecontrived；fortheymakethemovementofthespermaticsecretionsteadier，preservingthefoldingbackofthepassagesinthevivipara，ashorsesandthelike，andinman。（FordetailsseetheEnquiriesaboutAnimals。）Forthetestesarenopartoftheductsbutareonlyattachedtothem，aswomenfastenstonestotheloomwhenweaving；iftheyareremovedtheductsaredrawnupinternally，sothatcastratedanimalsareunabletogenerate；iftheywerenotdrawnuptheywouldbeable，andbeforenowabullmountingimmediatelyaftercastrationhascausedconceptioninthecowbecausetheductshadnotyetbeendrawnup。Inbirdsandoviparousquadrupedsthetestesreceivethespermaticsecretion，sothatitsexpulsionisslowerthaninfishes。Thisisclearinthecaseofbirds，fortheirtestesaremuchenlargedatthetimeofcopulation，andallthosewhichpairatoneseasonoftheyearhavethemsosmallwhenthisispastthattheyarealmostindiscernible，butduringtheseasontheyareverylarge。Whenthetestesareinternaltheactofcopulationisquickerthanwhentheyareexternal，foreveninthelattercasethesemenisnotemittedbeforethetestesaredrawnup。
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　　Besides，quadrupedshavetheorganofcopulation，sinceitispossibleforthemtohaveit，butforbirdsandthefootlessanimalsitisnotpossible，becausetheformerhavetheirlegsunderthemiddleoftheabdomenandthelatterhavenolegsatall；nowthepenisdependsfromthatregionandissituatedthere。（Whereforealsothelegsarestrainedinintercourse，boththepenisandthelegsbeingsinewy。）Sothat，sinceitisnotpossibleforthemtohavethisorgan，theymustnecessarilyeitherhavenotestesalso，oratanyratenothavethemthere，asthoseanimalsthathavebothpenisandtesteshavetheminthesamesituation。
　　Further，withthoseanimalsatanyratethathaveexternaltestes，thesemeniscollectedtogetherbeforeemission，andemissionisduetothepenisbeingheatedbyitsmovement；itisnotreadyforemissionatimmediatecontactasinfishes。
　　Allthevivipirahavetheirtestesinfront，internallyorexternally，exceptthehedgehog；healonehasthemneartheloin。Thisisforthesamereasonaswithbirds，becausetheirunionmustbequick，forthehedgehogdoesnot，liketheotherquadrupeds，mountuponthebackofthefemale，buttheyconjugatestandinguprightbecauseoftheirspines。
　　Somuchforthereasonswhythoseanimalshavetesteswhichhavethem，andwhytheyaresometimesexternalandsometimesinternal。
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　　Allthoseanimalswhichhavenotestesaredeficientinthispart，ashasbeensaid，notbecauseitisbettertobesobutsimplybecauseofnecessity，andsecondlybecauseitisnecessarythattheircopulationshouldbespeedy。Suchisthenatureoffishandserpents。Fishcopulatethrowingthemselvesalongsideofthefemalesandseparatingagainquickly。Forasmenandallsuchcreaturesmustholdtheirbreathbeforeemittingthesemen，sofishatsuchtimesmustceasetakinginthesea—water，andthentheyperisheasily。
　　Thereforetheymustnotmaturethesemenduringcopulation，asviviparousland—animalsdo，buttheyhaveitallmaturedtogetherbeforethetime，soasnottobematuringitwhileincontactbuttoemititreadymatured。Sotheyhavenotestes，andtheductsarestraightandsimple。Thereisasmallpartsimilartothisconnectedwiththetestesinthesystemofquadrupeds，forpartofthereflectedductissanguineousandpartisnot；thefluidisalreadysemenwhenitisreceivedbyandpassesthroughthislatterpart，sothatonceithasarrivedthereitissoonemittedinthesequadrupedsalso。Nowinfishesthewholepassageresemblesthelastsectionofthereflectedpartoftheductinmanandsimilaranimals。
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　　Serpentscopulatetwiningroundoneanother，and，assaidabove，haveneithertestesnorpenis，thelatterbecausetheyhavenolegs，theformerbecauseoftheirlength，buttheyhaveductslikeforonaccountoftheirextremelengththeseminalfluidwouldtaketoolonginitspassageandbecooledifitwerefurtherdelayedbytestes。（Thishappensalsoifthepenisislarge；suchmenarelessfertilethanwhenitissmallerbecausethesemen，ifcold，isnotgenerative，andthatwhichiscarriedtoofariscooled。）Somuchforthereasonwhysomeanimalshavetestesandothersnot。Serpentsintertwinebecauseoftheirinaptitudetocastthemselvesalongsideofoneanother。Fortheyaretoolongtounitecloselywithsosmallapartandhavenoorgansofattachment，sotheymakeuseofthesupplenessoftheirbodies，intertwining。Whereforealsotheyseemtobeslowerincopulationthanfish，notonlyonaccountofthelengthoftheductsbutalsoofthiselaboratearrangementinuniting。
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　　Itisnoteasytostatethefactsabouttheuterusinfemaleanimals，fortherearemanypointsofdifference。Theviviparaarenotalikeinthispart；womenandalltheviviparawithfeethavetheuteruslowdownbythepudendum，butthecartilaginousviviparousfishhaveithigherupnearthehypozoma。Intheovipara，again，itislowinfish（asinwomenandtheviviparousquadrupeds），highinbirdsandalloviparousquadrupeds。Yeteventhesedifferencesareonaprinciple。Tobeginwiththeovipara，theydifferinthemanneroflayingtheireggs，forsomeproducethemimperfect，asfisheswhoseeggsincreaseandarefinallydevelopedoutsideofthem。Thereasonisthattheyproducemanyyoung，andthisistheirfunctionasitiswithplants。Ifthentheyperfectedtheegginthemselvestheymustneedsbefewinnumber，butasitis，theyhavesomanythateachuterusseemstobeanegg，atanyrateinthesmallfishes。Forthesearethemostproductive，justaswiththeotheranimalsandplantswhosenatureisanalogoustotheirs，fortheincreaseofsizeturnswiththemtoseed。
　　Buttheeggsofbirdsandthequadrupedaloviparaareperfectwhenproduced。Inorderthatthesemaybepreservedtheymusthaveahardcovering（fortheirenvelopeissoftsolongastheyareincreasinginsize），andtheshellismadebyheatsqueezingoutthemoisturefortheearthymaterial；consequentlytheplacemustbehotinwhichthisistohappen。Butthepartaboutthehypozomaishot，asisshownbythatbeingthepartwhichconcoctsthefood。Ifthentheeggsmustbewithintheuterus，thentheuterusmustbenearthehypozomainthosecreatureswhichproducetheireggsinaperfectform。
　　Similarlyitmustbelowdowninthosewhichproducethemimperfect，foritisprofitablethatitshouldbeso。Anditismorenaturalfortheuterustobelowdownthanhighup，whenNaturehasnootherbusinessinhandtohinderit；foritsendislowdown，andwhereistheend，thereisthefunction，andtheuterusitselfisnaturallywherethefunctionis。
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　　Wefinddifferencesintheviviparaalsoascomparedwithoneanother。Someproducetheiryoungalive，notonlyexternally，butalsointernally，asmen，horses，dogs，andallthosewhichhavehair，andamongaquaticanimals，dolphins，whales，andsuchcetacea。
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　　Butthecartilaginousfishandthevipersproducetheiryoungaliveexternally，butfirstproduceeggsinternally。Theeggisperfect，forsoonlycanananimalbegeneratedfromanegg，andnothingcomesfromanimperfectone。Itisbecausetheyareofacoldnature，nothotassomeassert，thattheydonotlaytheireggsexternally。
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　　Atleasttheycertainlyproducetheireggsinasoftenvelope，thereasonbeingthattheyhavebutlittleheatandsotheirnaturedoesnotcompletetheprocessofdryingtheegg—shell。Because，then，theyarecoldtheyproducesoft—shelledeggs，andbecausetheeggsaresofttheydonotproducethemexternally；forthatwouldhavecausedtheirdestruction。
　　Theprocessisforthemostpartthesameasinbirds，fortheeggdescendsandtheyoungishatchedfromitnearthevagina，wheretheyoungisproducedinthoseanimalswhichareviviparousfromthebeginning。Thereforeinsuchanimalstheuterusisdissimilartothatofboththeviviparaandovipara，becausetheyparticipateinbothclasses；foritisatoncenearthehypozomaandalsostretchingalongdownwardsinallthecartilaginousfishes。ButthefactsaboutthisandtheotherkindsofuterusmustbegatheredfrominspectionofthedrawingsofdissectionsandfromtheEnquiries。
　　Thus，becausetheyareoviparous，layingperfecteggs，theyhavetheuterusplacedhigh，but，asbeingviviparous，low，participatinginbothclasses。
　　Animalsthatareviviparousfromthebeginningallhaveitlow，Natureherehavingnootherbusinesstointerferewithher，andtheirproductionhavingnodoublecharacter。Besidesthis，itisimpossibleforanimalstobeproducedalivenearthehypozoma，forthefoetusmustneedsbeheavyandmove，andthatregioninthemotherisvitalandwouldnotbeabletobeartheweightandthemovement。
　　Thirdly，parturitionwouldbedifficultbecauseofthelengthofthepassagetobetraversed；evenasitisthereisdifficultywithwomeniftheydrawuptheuterusinparturitionbyyawningoranythingofthekind，andevenwhenemptyitcausesafeelingofsuffocationifmovedupwards。Forifauterusistoholdalivinganimalitmustbestrongerthaninovipara，andthereforeinalltheviviparaitisfleshy，whereaswhentheuterusisnearthehypozomaitismembranous。
　　Andthisisclearalsointhecaseoftheanimalswhichproduceyoungbythemixedmethod，fortheireggsarehighupandsideways，butthelivingyoungareproducedinthelowerpartoftheuterus。
　　Somuchforthereasonwhydifferencesarefoundintheuterusofvariousanimals，andgenerallywhyitislowinsomeandhighinothersnearthehypozoma。
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　　Whyistheuterusalwaysinternal，butthetestessometimesinternal，sometimesexternal？Thereasonfortheuterusalwaysbeinginternalisthatinthisiscontainedtheeggorfoetus，whichneedsguarding，shelter，andmaturationbyconcoction，whiletheoutersurfaceofthebodyiseasilyinjuredandcold。Thetestesvaryinpositionbecausetheyalsoneedshelterandacoveringtopreservethemandtomaturethesemen；foritwouldbeimpossibleforthem，ifchilledandstiffened，tobedrawnupanddischargeit。
　　Therefore，wheneverthetestesarevisible，theyhaveacuticularcoveringknownasthescrotum。Ifthenatureoftheskinisopposedtothis，beingtoohardtobeadaptedforenclosingthemorforbeingsoftlikeatrue’skin’，aswiththescalyintegumentoffishandreptiles，thenthetestesmustneedsbeinternal。Thereforetheyaresoindolphinsandallthecetaceawhichhavethem，andintheoviparousquadrupedsamongthescalyanimals。Theskinofbirdsalsoishardsothatitwillnotconformtothesizeofanythingandencloseitneatly。（Thisisanotherreasonwithalltheseanimalsfortheirtestesbeinginternalbesidesthosepreviouslymentionedasarisingnecessarilyfromthedetailsofcopulation。）Forthesamereasontheyareinternalintheelephantandhedgehog，fortheskinofthese，too，isnotwellsuitedtokeeptheprotectivepartseparate。
　　[Thepositionoftheuterusdiffersinanimalsviviparouswithinthemselvesandthoseexternallyoviparous，andinthelatterclassagainitdiffersinthosewhichhavetheuteruslowandthosewhichhaveitnearthehypozoma，asinfishescomparedwithbirdsandoviparousquadrupeds。Anditisdifferentagaininthosewhichproduceyounginbothways，beingoviparousinternallyandviviparousexternally。Forthosewhichareviviparousbothinternallyandexternallyhavetheuterusplacedontheabdomen，asmen，cattle，dogs，andthelike，sinceitisexpedientforthesafetyandgrowthofthefoetusthatnoweightshouldbeupontheuterus。]
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　　Thepassagesalsoaredifferentthroughwhichthesolidandliquidexcretapassoutinallthevivipara。Whereforebothmalesandfemalesinthisclassallhaveapartwherebytheurineisvoided，andthisservesalsofortheissueofthesemeninmales，oftheoffspringinfemales。Thispassageissituatedaboveandinfrontofthepassageofthesolidexcreta。Thepassageisthesameasthatofthesolidnutrimentinallthoseanimalsthathavenopenis，inalltheovipara，eventhoseofthemthathaveabladder，asthetortoises。Foritisforthesakeofgeneration，notfortheevacuationoftheurine，thatthepassagesaredouble；butbecausethesemenisnaturallyliquid，theliquidexcretionalsosharesthesamepassage。Thisisclearfromthefactthatallanimalsproducesemen，butalldonotvoidliquidexcrement。Nowthespermaticpassagesofthemalemustbefixedandmustnotwander，andthesameappliestotheuterusofthefemale，andthisfixingmusttakeplaceateitherthefrontorthebackofthebody。Totaketheuterusfirst，itisinthefrontofthebodyinviviparabecauseofthefoetus，butattheloinandthebackinovipara。Allanimalswhichareinternallyoviparousandexternallyviviparousareinanintermediateconditionbecausetheyparticipateinbothclasses，beingatonceoviparousandviviparous。
　　Fortheupperpartoftheuterus，wheretheeggsareproduced，isunderthehypozomabytheloinandtheback，butasitadvancesislowattheabdomen；foritisinthatpartthattheanimalisviviparous。Inthesealsothepassageforsolidexcrementandforcopulationisthesame，fornoneofthese，ashasbeensaidalready，hasaseparatepudendum。
　　Thesameappliestothepassagesinthemale，whethertheyhavetestesorno，astotheuterusoftheovipara。Forinallofthem，notonlyintheovipara，theductsadheretothebackandtheregionofthespine。Fortheymustnotwanderbutbesettled，andthatisthecharacteroftheregionoftheback，whichgivescontinuityandstability。Nowinthosewhichhaveinternaltestes，theductsarefixedfromthefirst，andtheyarefixedinlikemannerifthetestesareexternal；thentheymeettogethertowardstheregionofthepenis。
　　Thelikeappliestotheductsinthedolphins，buttheyhavetheirtesteshiddenundertheabdominalcavity。
　　Wehavenowdiscussedthesituationofthepartscontributingtogeneration，andthecausesthereof。
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　　Thebloodlessanimalsdonotagreeeitherwiththesanguineaorwitheachotherinthefashionofthepartscontributingtogeneration。
　　Therearefourclassesstilllefttodealwith，firstthecrustacea，secondlythecephalopoda，thirdlytheinsects，andfourthlythetestacea。Wecannotbecertainaboutallofthem，butthatmostofthemcopulateisplain；inwhatmannertheyunitemustbestatedlater。
　　Thecrustaceacopulateliketheretromingentquadrupeds，fittingtheirtailstooneanother，theonesupineandtheotherprone。Fortheflapsattachedtothesidesofthetailbeinglongpreventthemfromunitingwiththebellyagainsttheback。Themaleshavefinespermaticducts，thefemalesamembranousuterusalongsidetheintestine，clovenoneachside，inwhichtheeggisproduced。
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　　Thecephalopodaentwinetogetheratthemouth，pushingagainstoneanotherandenfoldingtheirarms。Thisattitudeisnecessary，becauseNaturehasbentbackwardstheendoftheintestineandbroughtitroundnearthemouth，ashasbeensaidbeforeinthetreatiseonthepartsofanimals。Thefemalehasapartcorrespondingtotheuterus，plainlytobeseenineachoftheseanimals，foritcontainsaneggwhichisatfirstindivisibletotheeyebutafterwardssplitsupintomany；eachoftheseeggsisimperfectwhendeposited，aswiththeoviparousfishes。Inthecephalopoda（asalsointhecrustacea）thesamepassageservestovoidtheexcrementandleadstothepartlikeauterus，forthemaledischargestheseminalfluidthroughthispassage。Anditisonthelowersurfaceofthebody，wherethemantleisopenandthesea—waterentersthecavity。Hencetheunionofthemalewiththefemaletakesplaceatthispoint，foritisnecessary，ifthemaledischargeseithersemenorapartofhimselforanyotherforce，thatheshouldunitewithherattheuterinepassage。Buttheinsertion，inthecaseofthepoulps，ofthearmofthemaleintothefunnelofthefemale，bywhicharmthefishermensaythemalecopulateswithher，isonlyforthesakeofattachment，anditisnotanorganusefulforgeneration，foritisoutsidethepassageinthemaleandindeedoutsidethebodyofthemalealtogether。
　　Sometimesalsocephalopodaunitebythemalemountingonthebackofthefemale，butwhetherforgenerationorsomeothercausehasnotyetbeenobserved。
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　　Someinsectscopulateandtheoffspringareproducedfromanimalsofthesamename，justaswiththesanguinea；sucharethelocusts，cicadae，spiders，wasps，andants。Othersuniteindeedandgenerate；
　　buttheresultisnotacreatureofthesamekind，butonlyascolex，andtheseinsectsdonotcomeintobeingfromanimalsbutfromputrefyingmatter，liquidorsolid；sucharefleas，flies，andcantharides。Othersagainareneitherproducedfromanimalsnorunitewitheachother；sucharegnats，’conopes’，andmanysimilarkinds。Inmostofthosewhichunitethefemaleislargerthanthemale。Themalesdonotappeartohavespermaticpassages。Inmostcasesthemaledoesnotinsertanypartintothefemale，butthefemalefrombelowupwardsintothemale；thishasbeenobservedinmanycases（asalsothatthemalemountsthefemale），theoppositeinfewcases；butobservationsarenotyetcomprehensiveenoughtoenableustomakeadistinctionofclasses。Andgenerallyitistherulewithmostoftheoviparousfishandoviparousquadrupedsthatthefemaleislargerthanthebecausethisisexpedientinviewoftheincreaseofbulkinconceptionbyreasonoftheeggs。Inthefemalethepartanalogoustotheuterusiscleftandextendsalongtheintestine，aswiththeotheranimals；inthisareproducedtheresultsofconception。Thisisclearinlocustsandallotherlargeinsectswhosenatureitistounite；mostinsectsaretoosmalltobeobservedinthisrespect。
　　Suchisthecharacterofthegenerativeorgansinanimalswhichwerenotspokenofbefore。Itremainsnowtospeakofthehomogeneouspartsconcerned，theseminalfluidandmilk。Wewilltaketheformerfirst，andtreatofmilkafterwards。
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　　Someanimalsmanifestlyemitsemen，asallthesanguinea，butwhethertheinsectsandcephalopodadosoisuncertain。Thereforethisisaquestiontobeconsidered，whetherallmalesdoso，ornotall；
　　andifnotall，whysomedoandsomenot；andwhetherthefemalealsocontributesanysemenornot；and，ifnotsemen，whethershedoesnotcontributeanythingelseeither，orwhethershecontributessomethingelsewhichisnotsemen。Wemustalsoinquirewhatthoseanimalswhichemitsemencontributebymeansofittogeneration，andgenerallywhatisthenatureofsemen，andoftheso—calledcatameniainallanimalswhichdischargethisliquid。
　　Nowitisthoughtthatallanimalsaregeneratedoutofsemen，andthatthesemencomesfromtheparents。Whereforeitispartofthesameinquirytoaskwhetherbothmaleandfemaleproduceitoronlyoneofthem，andtoaskwhetheritcomesfromthewholeofthebodyornotfromthewhole；forifthelatteristrueitisreasonabletosupposethatitdoesnotcomefrombothparentseither。Accordingly，sincesomesaythatitcomesfromthewholeofthebody，wemustinvestigatethisquestionfirst。
　　Theproofsfromwhichitcanbearguedthatthesemencomesfromeachandeverypartofthebodymaybereducedtofour。First，theintensityofthepleasureofcoition；forthesamestateoffeelingismorepleasantifmultiplied，andthatwhichaffectsallthepartsismultipliedascomparedwiththatwhichaffectsonlyoneorafew。
　　Secondly，theallegedfactthatmutilationsareinherited，fortheyarguethatsincetheparentisdeficientinthispartthesemendoesnotcomefromthence，andtheresultisthatthecorrespondingpartisnotformedintheoffspring。Thirdly，theresemblancestotheparents，fortheyoungarebornlikethempartforpartaswellasinthewholebody；ifthenthecomingofthesemenfromthewholebodyiscauseoftheresemblanceofthewhole，sothepartswouldbelikebecauseitcomesfromeachoftheparts。Fourthly，itwouldseemtobereasonabletosaythatasthereissomefirstthingfromwhichthewholearises，soitisalsowitheachoftheparts，andthereforeifsemenorseediscauseofthewholesoeachofthepartswouldhaveaseedpeculiartoitself。Andtheseopinionsareplausiblysupportedbysuchevidenceasthatchildrenarebornwithalikenesstotheirparents，notincongenitalbutalsoinacquiredcharacteristics；forbeforenow，whentheparentshavehadscars，thechildrenhavebeenbornwithamarkintheformofthescarinthesameplace，andtherewasacaseatChalcedonwherethefatherhadabrandonhisarmandtheletterwasmarkedonthechild，onlyconfusedandnotclearlyarticulated。
　　Thatisprettymuchtheevidenceonwhichsomebelievethatthesemencomesfromallthebody。
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　　Onexaminingthequestion，however，theoppositeappearsmorelikely，foritisnothardtorefutetheaboveargumentsandtheviewinvolvesimpossibilities。First，then，theresemblanceofchildrentoparentsisnoproofthatthesemencomesfromthewholebody，becausetheresemblanceisfoundalsoinvoice，nails，hair，andwayofmoving，fromwhichnothingcomes。Andmengeneratebeforetheyyethavecertaincharacters，suchasabeardorgreyhair。
　　Further，childrenareliketheirmoreremoteancestorsfromwhomnothinghascome，fortheresemblancesrecuratanintervalofmanygenerations，asinthecaseofthewomaninEliswhohadintercoursewiththeAethiop；herdaughterwasnotanAethiopbutthesonofthatdaughterwas。Thesamethingappliesalsotoplants，foritisclearthatifthistheoryweretruetheseedwouldcomefromallpartsofplantsalso；butoftenaplantdoesnotpossessonepart，andanotherpartmayberemoved，andathirdgrowsafterwards。Besides，theseeddoesnotcomefromthepericarp，andyetthisalsocomesintobeingwiththesameformasintheparentplant。
　　Wemayalsoaskwhetherthesemencomesfromeachofthehomogeneouspartsonly，suchasfleshandboneandsinew，oralsofromtheheterogeneous，suchasfaceandhands。Foriffromtheformeronly，weobjectthatresemblanceexistsratherintheheterogeneousparts，suchasfaceandhandsandfeet；ifthenitisnotbecauseofthesemencomingfromallpartsthatchildrenresembletheirparentsinthese，whatistheretostopthehomogeneouspartsalsofrombeinglikeforsomeotherreasonthanthis？Ifthesemencomesfromtheheterogeneousalone，thenitdoesnotcomefromallparts；butitismorefittingthatitshouldcomefromthehomogeneousparts，fortheyarepriortotheheterogeneouswhicharecomposedofthem；andaschildrenarebornliketheirparentsinfaceandhands，sotheyare，necessarily，infleshandnails。Ifthesemencomesfromboth，whatwouldbethemannerofgeneration？Fortheheteroeneouspartsarecomposedofthehomogneous，sothattocomefromtheformerwouldbetocomefromthelatterandfromtheircomposition。Tomakethisclearerbyanillustration，takeawrittenname；ifanythingcamefromthewholeofit，itwouldbefromeachofthesyllables，andiffromthese，fromthelettersandtheircomposition。Sothatifreallyfleshandbonesarecomposedoffireandthelikeelements，thesemenwouldcomeratherfromtheelementsthananythingelse，forhowcanitcomefromtheircomposition？Yetwithoutthiscompositiontherewouldbenoresemblance。Ifagainsomethingcreatesthiscompositionlater，itwouldbethisthatwouldbethecauseoftheresemblance，notthecomingofthesemenfromeverypartofthebody。
　　Further，ifthepartsofthefutureanimalareseparatedinthesemen，howdotheylive？andiftheyareconnected，theywouldformasmallanimal。
　　Andwhataboutthegenerativeparts？Forthatwhichcomesfromthemaleisnotsimilartowhatcomesfromthefemale。
　　Again，ifthesemencomesfromallpartsofbothparentsalike，theresultistwoanimals，fortheoffspringwillhaveallthepartsofboth。WhereforeEmpedoclesseemstosaywhatagreesprettywellwiththisview（ifwearetoadoptit），toacertainextentatanyrate，buttobewrongifwethinkotherwise。Whathesaysagreeswithitwhenhedeclaresthatthereisasortoftallyinthemaleandfemale，andthatthewholeoffspringdoesnotcomefromeither，’butsunderedisthefashionoflimbs，someinman’s……’Forwhydoesnotthefemalegeneratefromherselfifthesemencomesfromallpartsalikeandshehasareceptaclereadyintheuterus？But，itseems，eitheritdoesnotcomefromalltheparts，orifitdoesitisinthewayEmpedoclessays，notthesamepartscomingfromeachparent，whichiswhytheyneedintercoursewitheachother。
　　Yetthisalsoisimpossible，justasmuchasitisimpossibleforthepartswhenfullgrowntosurviveandhavelifeinthemwhentornapart，asEmpedoclesaccountsforthecreationofanimals；inthetimeofhis’ReignofLove’，sayshe，’manyheadssprangupwithoutnecks，’
　　andlaterontheseisolatedpartscombinedintoanimals。Nowthatthisisimpossibleisplain，forneitherwouldtheseparatepartsbeabletosurvivewithouthavinganysoulorlifeinthem，noriftheywerelivingthings，sotosay，couldseveralofthemcombinesoastobecomeoneanimalagain。Yetthosewhosaythatsemencomesfromthewholeofthebodyreallyhavetotalkinthatway，andasithappenedthenintheearthduringthe’ReignofLove’，soithappensaccordingtotheminthebody。Nowitisimpossiblethatthepartsshouldbeunitedtogetherwhentheycomeintobeingandshouldcomefromdifferentpartsoftheparent，meetingtogetherinoneplace。
　　Thenhowcantheupperandlower，rightandleft，frontandbackpartshavebeen’sundered’？Allthesepointsareunintelligible。Further，somepartsaredistinguishedbypossessingafaculty，othersbybeingincertainstatesorconditions；theheterogeneous，astongueandhand，bythefacultyofdoingsomething，thehomogeneousbyhardnessandsoftnessandtheothersimilarstates。Blood，then，willnotbeblood，norfleshflesh，inanyandeverystate。Itisclear，then，thatthatwhichcomesfromanypart，asbloodfrombloodorfleshfromflesh，willnotbeidenticalwiththatpart。Butifitissomethingdifferentfromwhichthebloodoftheoffspringcomes，thecomingofthesemenfromallthepartswillnotbethecauseoftheresemblance，asisheldbythesupportersofthistheory。
　　Forifbloodisformedfromsomethingwhichisnotblood，itisenoughthatthesemencomefromonepartonly，forwhyshouldnotalltheotherpartsoftheoffspringaswellasbloodbeformedfromonepartoftheparent？Indeed，thistheoryseemstobethesameasthatofAnaxagoras，thatnoneofthehomogeneouspartscomeintobeing，exceptthatthesetheoristsassume，inthecaseofthegenerationofanimals，whatheassumedoftheuniverse。
　　Then，again，howwillthesepartsthatcamefromallthebodyoftheparentbeincreasedorgrow？ItistruethatAnaxagorasplausiblysaysthatparticlesoffleshoutofthefoodareaddedtotheflesh。Butifwedonotsaythis（whilesayingthatsemencomesfromallpartsofthebody），howwillthefoetusbecomegreaterbytheadditionofsomethingelseifthatwhichisaddedremainunchanged？Butifthatwhichisaddedcanchange，thenwhynotsaythatthesemenfromtheveryfirstisofsuchakindthatbloodandfleshcanbemadeoutofit，insteadofsayingthatititselfisbloodandflesh？Noristhereanyotheralternative，forsurelywecannotsaythatitisincreasedlaterbyaprocessofmixing，aswinewhenwaterispouredintoit。Forinthatcaseeachelementofthemixturewouldbeitselfatfirstwhilestillunmixed，butthefactratheristhatfleshandboneandeachoftheotherpartsissuchlater。Andtosaythatsomepartofthesemenissinewandboneisquiteaboveus，asthesayingis。
　　Besidesallthisthereisadifficultyifthesexisdeterminedinconception（asEmpedoclessays：’itisshedincleanvessels；somewaxfemale，iftheyfallinwithcold’）。Anyhow，itisplainthatbothmenandwomenchangenotonlyfrominfertiletofertile，butalsofrombearingfemaletobearingmaleoffspring，whichlooksasifthecausedoesnotlieinthesemencomingfromalltheparentornot，butinthemutualproportionordisproportionofthatcomesfromthewomanandtheman，orinsomethingofthiskind。Itisclear，then，ifwearetoputthisdownasbeingso，thatthefemalesexisnotdeterminedbythesemencomingfromanyparticularpart，andconsequentlyneitheristhespecialsexualpartsodetermined（ifreallythesamesemencanbecomeeithermaleorfemalechild，whichshowsthatthesexualpartdoesnotexistinthesemen）。Why，then，shouldweassertthisofthispartanymorethanofothers？Forifsemendoesnotcomefromthispart，theuterus，thesameaccountmaybegivenoftheothers。
　　Again，somecreaturescomeintobeingneitherfromparentsofthesamekindnorfromparentsofadifferentkind，asfliesandthevariouskindsofwhatarecalledfleas；fromtheseareproducedanimalsindeed，butnotinthiscaseofsimilarnaturebutakindofscolex。Itisplaininthiscasethattheyoungofadifferentkindarenotproducedbysemencomingfromallpartsoftheparent，fortheywouldthenresemblethem，ifindeedresemblanceisasignofitscomingfromallparts。
　　Furtherevenamonganimalssomeproducemanyyoungfromasinglecoition（andsomethinglikethisisuniversalamongplants，foritisplainthattheybearallthefruitofawholeseasonfromasinglemovement）。Andyethowwouldthisbepossibleifthesemenweresecretedfromallthebody？Forfromasinglecoitionandasinglesegregationofthesemenscatteredthroughoutthebodymustneedsfollowonlyasinglesecretion。Norisitpossibleforittobeseparatedintheuterus，forthiswouldnolongerbeamereseparationofsemen，but，asitwere，aseverancefromanewplantoranimal。
　　Again，thecuttingsfromaplantbearseed；clearly，therefore，evenbeforetheywerecutfromtheparentplant，theyboretheirfruitfromtheirownmassalone，andtheseeddidnotcomefromalltheplant。
　　Butthegreatestproofofallisderivedfromobservationswehavesufficientlyestablishedoninsects。For，ifnotinall，atleastinmostofthese，thefemaleintheactofcopulationinsertsapartofherselfintothemale。This，aswesaidbefore，isthewaytheycopulate，forthefemalesmanifestlyinsertthisfrombelowintothemalesabove，notinallcases，butinmostofthoseobserved。Henceitseemsclearthat，whenthemalesdoemitsemen，thenalsothecauseofthegenerationisnotitscomingfromallthebody，butsomethingelsewhichmustbeinvestigatedhereafter。Forevenifitweretruethatitcomesfromallthebody，astheysay，theyoughtnottoclaimthatitcomesfromallpartsofit，butonlyfromthecreativepart—fromtheworkman，sotosay，notthematerialheworksin。Insteadofthat，theytalkasifoneweretosaythatthesemencomesfromtheshoes，for，generallyspeaking，ifasonislikehisfather，theshoeshewearsarelikehisfather’sshoes。
　　Astothevehemenceofpleasureinsexualintercourse，itisnotbecausethesemencomesfromallthebody，butbecausethereisastrongfriction（whereforeifthisintercourseisoftenrepeatedthepleasureisdiminishedinthepersonsconcerned）。Moreover，thepleasureisattheendoftheact，butitought，onthetheory，tobeineachoftheparts，andnotatthesametime，butsoonerinsomeandlaterinothers。
　　Ifmutilatedyoungarebornofmutilatedparents，itisforthesamereasonasthatforwhichtheyarelikethem。Andtheyoungofmutilatedparentsarenotalwaysmutilated，justastheyarenotalwaysliketheirparents；thecauseofthismustbeinquiredintolater，forthisproblemisthesameasthat。
　　Again，ifthefemaledoesnotproducesemen，itisreasonabletosupposeitdoesnotcomefromallthebodyofthemaleeither。
　　Conversely，ifitdoesnotcomefromallthemaleitisnotunreasonabletosupposethatitdoesnotcomefromthefemale，butthatthefemaleiscauseofthegenerationinsomeotherway。Intothiswemustnextinquire，sinceitisplainthatthesemenisnotsecretedfromalltheparts。
　　Inthisinvestigationandthosewhichfollowfromit，thefirstthingtodoistounderstandwhatsemenis，forthenitwillbeeasiertoinquireintoitsoperationsandthephenomenaconnectedwithit。
　　Nowtheobjectofsemenistobeofsuchanaturethatfromitastheirorigincomeintobeingthosethingswhicharenaturallyformed，notbecausethereisanyagentwhichmakesthemfromitassimplybecausethisisthesemen。Nowwespeakofonethingcomingfromanotherinmanysenses；itisonethingwhenwesaythatnightcomesfromdayoramanbecomesmanfromboy，meaningthatAfollowsB；itisanotherifwesaythatastatueismadefrombronzeandabedfromwood，andsooninalltheothercaseswherewesaythatthethingmadeismadefromamaterial，meaningthatthewholeisformedfromsomethingpreexistingwhichisonlyputintoshape。Inathirdsenseamanbecomesunmusicalfrombeingmusical，sickfrombeingwell，andgenerallyinthissensecontrariesarisefromcontraries。
　　Fourthly，asinthe’climax’ofEpicharmus；thusfromslandercomesrailingandfromthisfighting，andallthesearefromsomethinginthesensethatitistheefficientcause。Inthislastclasssometimestheefficientcauseisinthethingsthemselves，asinthelastmentioned（fortheslanderisapartofthewholetrouble），andsometimesexternal，astheartisexternaltotheworkofartorthetorchtotheburninghouse。Nowtheoffspringcomesfromthesemen，anditisplainlyinoneofthetwofollowingsensesthatitdoesso—eitherthesemenisthematerialfromwhichitismade，oritisthefirstefficientcause。ForassuredlyitisnotinthesenseofA
　　beingafterB，asthevoyagecomesfrom，i。e。after，thePanathenaea；noryetascontrariescomefromcontraries，forthenoneofthetwocontrariesceasestobe，andathirdsubstancemustexistasanimmediateunderlyingbasisfromwhichthenewthingcomesintobeing。Wemustdiscoverthen，inwhichofthetwootherclassesthesemenistobeput，whetheritistoberegardedasmatter，andthereforeacteduponbysomethingelse，orasaform，andthereforeactinguponsomethingelse，orasbothatonce。Forperhapsatthesametimeweshallseeclearlyalsohowalltheproductsofsemencomeintobeingfromcontraries，sincecomingintobeingfromcontrariesisalsoanaturalprocess，forsomeanimalsdoso，i。e。frommaleandfemale，othersfromonlyoneparent，asisthecasewithplantsandallthoseanimalsinwhichmaleandfemalearenotseparatelydifferentiated。Nowthatwhichcomesfromthegeneratingparentiscalledtheseminalfluid，beingthatwhichfirsthasinitaprincipleofgeneration，inthecaseofallanimalswhosenatureitistounite；semenisthatwhichhasinittheprinciplesfrombothunitedparents，asthefirstmixturewhicharisesfromtheunionofmaleandfemale，beitafoetusoranovum，forthesealreadyhaveinthemthatwhichcomesfromboth。（Semen，orseed，andgraindifferonlyintheonebeingearlierandtheotherlater，graininthatitcomesfromsomethingelse，i。e。theseed，andseedinthatsomethingelse，thegrain，comesfromit，forbotharereallythesamething。）
　　Wemustagaintakeupthequestionwhattheprimarynatureofwhatiscalledsemenis。Needsmusteverythingwhichwefindinthebodyeitherbe（1）oneofthenaturalparts，whetherhomogeneousorheterogeneous，or（2）anunnaturalpartsuchasagrowth，or（3）asecretionorexcretion，or（4）waste—product，or（5）nutriment。（BysecretionorexcretionImeantheresidueofthenutriment，bywaste—productthatwhichisgivenofffromthetissuesbyanunnaturaldecomposition。）
　　Nowthatsemencannotbeapartofthebodyisplain，foritishomogeneous，andfromthehomogeneousnothingiscomposed，e。g。fromonlysineworonlyflesh；norisitseparatedasarealltheotherparts。ButneitherisitcontrarytoNaturenoradefect，foritexistsinallalike，andthedevelopmentoftheyounganimalcomesfromit。Nutriment，again，isobviouslyintroducedfromwithout。
　　Itremains，then，thatitmustbeeitherawaste—productorasecretionorexcretion。Nowtheancientsseemtothinkthatitisawaste—product，forwhentheysaythatitcomesfromallthebodybyreasonoftheheatofthemovementofthebodyincopulation，theyimplythatitisakindofwaste—product。ButthesearecontrarytoNature，andfromsucharisesnothingaccordingtoNature。Sothenitmustbeasecretionorexcretion。
　　But，togofurtherintoit，everysecretionorexcretioniseitherofuselessorusefulnutriment；by’useless’Imeanthatfromwhichnothingfurtheriscontributedtonaturalgrowth，butwhichisparticularlymischievoustothebodyiftoomuchofitisconsumed；by’useful’Imeantheopposite。Nowitisevidentthatitcannotbeoftheformercharacter，forsuchismostabundantinpersonsoftheworstconditionofbodythroughageorsickness；semen，onthecontrary，isleastabundantinthemforeithertheyhavenoneatalloritisnotfertile，becauseauselessandmorbidsecretionismingledwithit。
　　Semen，then，ispartofausefulsecretion。Butthemostusefulisthelastandthatfromwhichfinallyisformedeachofthepartsofthebody。Forsecretionsareeitherearlierorlater；ofthenutrimentinthefirststagethesecretionisphlegmandthelike，forphlegmalsoisasecretionoftheusefulnutriment，anindicationofthisbeingthatifitismixedwithpurenutrimentitisnourishing，andthatitisusedupincasesofillness。Thefinalsecretionisthesmallestinproportiontothequantityofnutriment。Butwemustreflectthatthedailynutrimentbywhichanimalsandplantsgrowisbutsmall，forifaverylittlebeaddedcontinuallytothesamethingthesizeofitwillbecomeexcessive。
　　Sowemustsaytheoppositeofwhattheancientssaid。Forwhereastheysaidthatsemenisthatwhichcomesfromallthebody，weshallsayitisthatwhosenatureistogotoallofit，andwhattheythoughtawaste—productseemsrathertobeasecretion。Foritismorereasonabletosupposethatthelastextractofthenutrimentwhichgoestoallpartsresemblesthatwhichisleftoverfromit，justaspartofapainter’scolourisoftenleftoverresemblingthatwhichhehasusedup。Waste—products，onthecontrary，arealwaysduetocorruptionordecayandtoadeparturefromNature。
　　Afurtherproofthatitisnotawaste—product，butratherasecretion，isthefactthatthelargeanimalshavefewyoung，thesmallmany。Forthelargemusthavemorewasteandlesssecretion，sincethegreatsizeofthebodycausesmostofthenutrimenttobeusedup，sothattheresidueorsecretionissmall。
　　Again，noplacehasbeensetapartbyNatureforwaste—productsbuttheyflowwherevertheycanfindaneasypassageinthebody，butaplacehasbeensetapartforallthenaturalsecretions；thusthelowerintestineservesfortheexcretionofthesolidnutriment，thebladderforthatoftheliquid；fortheusefulpartofthenutrimentwehavetheupperintestine，forthespermaticsecretionstheuterusandpudendaandbreasts，foritiscollectedandflowstogetherintothem。
　　Andtheresultingphenomenaareevidencethatsemeniswhatwehavesaid，andtheseresultbecausesuchisthenatureofthesecretion。Fortheexhaustionconsequentonthelossofevenaverylittleofthesemenisconspicuousbecausethebodyisdeprivedoftheultimategaindrawnfromthenutriment。Withsomefewpersons，itistrue，duringashorttimeinthefloweroftheiryouththelossofit，ifitbeexcessiveinquantity，isanalleviation（justasinthecaseofthenutrimentinitsfirststage，iftoomuchhavebeentaken，sincegettingridofthisalsomakesthebodymorecomfortable），andsoitmaybealsowhenothersecretionscomeawaywithit，forinthatcaseitisnotonlysementhatislostbutalsootherinfluencescomeawaymingledwithit，andthesearemorbid。Wherefore，withsomemenatleast，thatwhichcomesfromthemprovessometimesincapableofprocreationbecausetheseminalelementinitissosmall。Butstillinmostmenandasageneralruletheresultofintercourseisexhaustionandweaknessratherthanrelief，forthereasongiven。Moreover，semendoesnotexistinthemeitherinchildhoodorinoldageorinsickness—inthelastcasebecauseofweakness，inoldagebecausetheydonotsufficientlyconcocttheirfood，andinchildhoodbecausetheyaregrowingandsoallthenutrimentisuseduptoosoon，forinaboutfiveyears，inthecaseofhumanbeingsatanyrate，thebodyseemstogainhalftheheightthatisgainedinalltherestoflife。
　　Inmanyanimalsandplantswefindadifferenceinthisconnexionnotonlybetweenkindsascomparedwithkinds，butalsobetweensimilarindividualsofthesamekindascomparedwitheachother，e。g。
　　manwithmanorvinewithvine。Somehavemuchsemen，otherslittle，othersagainnoneatall，notthroughweaknessbutthecontrary，atanyrateinsomecases。Thisisbecausethenutrimentisuseduptoformthebody，aswithsomehumanbeings，who，beingingoodconditionanddevelopingmuchfleshorgettingrathertoofat，producelesssemenandarelessdesirousofintercourse。Likethisiswhathappenswiththosevineswhich’playthegoat’，thatis，luxuriatewantonlythroughtoomuchnutrition，forhe—goatswhenfatarelessinclinedtomountthefemale；forwhichreasontheythinthembeforebreedingfromthem，andsaythatthevines’playthegoat’，socallingitfromtheconditionofthegoats。Andfatpeople，womenaswellasmen，appeartobelessfertilethanothersfromthefactthatthesecretionwheninprocessofconcoctionturnstofatwiththosewhoaretoowell—nourished。Forfatalsoisahealthysecretionduetogoodliving。
　　Insomecasesnosemenisproducedatall，asbythewillowandpoplar。Thisconditionisduetoeachofthetwocauses，weaknessandstrength；theformerpreventsconcoctionofthenutriment，thelattercausesittobeallconsumed，assaidabove。Inlikemannerotheranimalsproducemuchsementhroughweaknessaswellasthroughstrength，whenagreatquantityofauselesssecretionismixedwithit；thissometimesresultsinactualdiseasewhenapassageisnotfoundtocarryofftheimpurity，andthoughsomerecoverofthis，othersactuallydieofit。Forcorrupthumourscollecthereasintheurine，whichalsohasbeenknowntocausedisease。