Anditagreeswithourviewsthatthebeesattendupontheirkingsbecausetheyaretheiroffspring（forifnothingofthesorthadbeenthecasethefactsabouttheirleadershipwouldbeunreasonable），andthat，whiletheysufferthekingstodonoworkasbeingtheirparents，theypunishthedronesastheirchildren，foritisnoblertopunishone’schildrenandthosewhohavenoworktoperform。Thefactthattheleaders，beingfew，generatethebeesinlargenumbersseemstobesimilartowhatobtainsinthegenerationoflions，whichatfirstproducefive，afterwardsasmallernumbereachtimeatlastoneandthereafternone。Sotheleadersatfirstproduceanumberofworkers，afterwardsafewoftheirownkind；thusthebroodofthelatterissmallerinnumberthanthatoftheformer，butwhereNaturehastakenawayfromtheminnumbershehasmadeitupagaininsize。
　　Suchappearstobethetruthaboutthegenerationofbees，judgingfromtheoryandfromwhatarebelievedtobethefactsaboutthem；thefacts，however，havenotyetbeensufficientlygrasped；ifevertheyare，thencreditmustbegivenrathertoobservationthantotheories，andtotheoriesonlyifwhattheyaffirmagreeswiththeobservedfacts。
　　Afurtherindicationthatbeesareproducedwithoutcopulationisthefactthatthebroodappearssmallinthecellsofthecomb，whereas，wheneverinsectsaregeneratedbycopulation，theparentsremainunitedforalongtimebutproducequicklysomethingofthenatureofascolexandofaconsiderablesize。
　　Concerningthegenerationofanimalsakintothem，ashornetsandwasps，thefactsinallcasesaresimilartoacertainextent，butaredevoidoftheextraordinaryfeatureswhichcharacterizebees；thisweshouldexpect，fortheyhavenothingdivineaboutthemasthebeeshave。Fortheso—called’mothers’generatetheyoungandmouldthefirstpartofthecombs，buttheygeneratebycopulationwithoneanother，fortheirunionhasoftenbeenobserved。Asforallthedifferencesofeachofthesekindfromoneanotherandfrombees，theymustbeinvestigatedwiththeaidoftheillustrationstotheEnquiries。
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　　Havingspokenofthegenerationofallinsects，wemustnowspeakofthetestacea。Herealsothefactsofgenerationarepartlylikeandpartlyunlikethoseintheotherclasses。Andthisiswhatmightbeexpected。Forcomparedwithanimalstheyresembleplants，comparedwithplantstheyresembleanimals，sothatinasensetheyappeartocomeintobeingfromsemen，butinanothersensenotso，andinonewaytheyarespontaneouslygeneratedbutinanotherfromtheirownkind，orsomeoftheminthelatterway，othersintheformer。Becausetheirnatureanswerstothatofplants，thereforefewornokindsoftestaceacomeintobeingonland，e。g。thesnailsandanyothers，fewastheyare，thatresemblethem；butintheseaandsimilarwaterstherearemanyofallkindsofforms。Buttheclassofplantshasbutfewandonemaysaypracticallynorepresentativesintheseaandsuchplaces，allsuchgrowingontheland。Forplantsandtestaceaareanalogous；andinproportionasliquidhasmorequickeningpowerthansolid，waterthanearth，somuchdoesthenatureoftestaceadifferfromthatofplants，sincetheobjectoftestaceaistobeinsucharelationtowaterasplantsaretoearth，asifplantswere，sotosay，land—oysters，oysterswater—plants。
　　Forsuchareasonalsothetestaceainthewatervarymoreinformthanthoseontheland。Forthenatureofliquidismoreplasticthanthatofearthandyetnotmuchlessmaterial，andthisisespeciallytrueoftheinhabitantsofthesea，forfreshwater，thoughsweetandnutritious，iscoldandlessmaterial。Whereforeanimalshavingnobloodandnotofahotnaturearenotproducedinlakesnorinthefresheramongbrackishwaters，butonlyexceptionally，butitisinestuariesandatthemouthsofriversthattheycomeintobeing，astestaceaandcephalopodaandcrustacea，allthesebeingbloodlessandofacoldnature。Fortheyseekatthesametimethewarmthofthesunandfood；nowtheseaisnotonlywaterbutmuchmorematerialthanfreshwaterandhotinitsnature；ithasashareinallthepartsoftheuniverse，waterandairandearth，sothatitalsohasashareinalllivingthingswhichareproducedinconnexionwitheachoftheseelements。Plantsmaybeassignedtoland，theaquaticanimalstowater，thelandanimalstoair，butvariationsofquantityanddistancemakeagreatandwonderfuldifference。Thefourthclassmustnotbesoughtintheseregions，thoughtherecertainlyoughttobesomeanimalcorrespondingtotheelementoffire，forthisiscountedinasthefourthoftheelementarybodies。Buttheformwhichfireassumesneverappearstobepeculiartoit，butitalwaysexistsinsomeotheroftheelements，forthatwhichisignitedappearstobeeitherairorsmokeorearth。Suchakindofanimalmustbesoughtinthemoon，forthisappearstoparticipateintheelementremovedinthethirddegreefromearth。Thediscussionofthesethingshoweverbelongstoanothersubject。
　　Toreturntotestacea，someofthemareformedspontaneously，someemitasortofgenerativesubstancefromthemselves，butthesealsooftencomeintobeingfromaspontaneousformation。Tounderstandthiswemustgraspthedifferentmethodsofgenerationinplants；someoftheseareproducedfromseed，somefromslips，plantedout，somebybuddingoffalongside，astheclassofonions。Inthelastwayproducedmussels，forsmalleronesarealwaysgrowingoffalongsidetheoriginal，butthewhelks，thepurple—fish，andthosewhicharesaidto’spawn’emitmassesofaliquidslimeasiforiginatedbysomethingofaseminalnature。Wemustnot，however，considerthatanythingofthesortisrealsemen，butthatthesecreaturesparticipateintheresemblancetoplantsinthemannerstatedabove。
　　Hencewhenonceonesuchcreaturehasbeenproduced，thenisproducedanumberofthem。Forallthesecreaturesareliabletobeevenspontaneouslygenerated，andsotobeformedstillmoreplentifullyinproportionifsomearealreadyexisting。Foritisnaturalthateachshouldhavesomesuperfluousresidueattachedtoitfromtheoriginal，andfromthisbudsoffeachofthecreaturesgrowingalongsideofit。Again，sincethenutrimentanditsresiduepossessalikepower，itislikelythattheproductofthosetestaceawhich’spawn’shouldresembletheoriginalformation，andsoitisnaturalthatanewanimalofthesamekindshouldcomeintobeingfromthisalso。
　　Allthosewhichdonotbudoffor’spawn’arespontaneouslygenerated。Nowallthingsformedinthisway，whetherinearthorwater，manifestlycomeintobeinginconnexionwithputrefactionandanadmixtureofrain—water。Forasthesweetisseparatedoffintothematterwhichisforming，theresidueofthemixturetakessuchaform。
　　Nothingcomesintobeingbyputrefying，butbyconcocting；
　　putrefactionandthethingputrefiedisonlyaresidueofthatwhichisconcocted。Fornothingcomesintobeingoutofthewholeofanything，anymorethanintheproductsofart；ifitdidartwouldhavenothingtodo，butasitisintheonecaseartremovestheuselessmaterial，intheotherNaturedoesso。Animalsandplantscomeintobeinginearthandinliquidbecausethereiswaterinearth，andairinwater，andinallairisvitalheatsothatinasenseallthingsarefullofsoul。Thereforelivingthingsformquicklywheneverthisairandvitalheatareenclosedinanything。Whentheyaresoenclosed，thecorporealliquidsbeingheated，therearisesasitwereafrothybubble。Whetherwhatisformingistobemoreorlesshonourableinkinddependsontheembracingofthepsychicalprinciple；thisagaindependsonthemediuminwhichthegenerationtakesplaceandthematerialwhichisincluded。Nowintheseatheearthymatterispresentinlargequantities，andconsequentlythetestaceousanimalsareformedfromaconcretionofthiskind，theearthymatterhardeningroundthemandsolidifyinginthesamemannerasbonesandhorns（forthesecannotbemeltedbyfire），andthematter（orbody）whichcontainsthelifebeingincludedwithinit。
　　Theclassofsnailsistheonlyclassofsuchcreaturesthathasbeenseenuniting，butithasneveryetbeensufficientlyobservedwhethertheirgenerationistheresultoftheunionornot。
　　Itmaybeasked，ifwewishtofollowtherightlineofinvestigation，whatitisinsuchanimalstheformationofwhichcorrespondstothematerialprinciple。Forinthefemalesthisisaresidualsecretionoftheanimal，potentiallysuchasthatfromwhichitcame，byimpartingmotiontowhichtheprinciplederivedfromthemaleperfectstheanimal。Butherewhatmustbesaidtocorrespondtothis，andwhencecomesorwhatisthemovingprinciplewhichcorrespondstothemale？Wemustunderstandthateveninanimalswhichgenerateitisfromtheincomingnourishmentthattheheatintheanimalmakestheresidue，thebeginningoftheconception，bysecretionandconcoction。Thelikeisthecasealsoinplants，exceptthatinthese（andalsoinsomeanimals）thereisnofurtherneedofthemaleprinciple，becausetheyhaveitmingledwiththefemaleprinciplewithinthemselves，whereastheresidualsecretioninmostanimalsdoesneedit。Thenourishmentagainofsomeisearthandwater，ofothersthemorecomplicatedcombinationsofthese，sothatwhattheheatinanimalsproducesfromtheirnutriment，thisdoestheheatofthewarmseasonintheenvironmentputtogetherandcombinebyconcoctionoutofthesea—waterontheearth。Andtheportionofthepsychicalprinciplewhichiseitherincludedalongwithitorseparatedoffintheairmakesanembryoandputsmotionintoit。Nowinplantswhicharespontaneouslygeneratedthemethodofformationisuniform；theyarisefromapartofsomething，andwhilesomeofitisthestarting—pointoftheplant，someisthefirstnourishmentoftheyoungshoots……Otheranimalsareproducedintheformofascolex，notonlythosebloodlessanimalswhicharenotgeneratedfromparentsbutevensomesanguinea，asakindofmulletandsomeotherriverfishesandalsotheeelkind。
　　Forallofthese，thoughtheyhavebutlittlebloodbynature，areneverthelesssanguinea，andhaveaheartwithbloodinitastheoriginoftheparts；andtheso—called’entrailsofearth’，inwhichcomesintobeingthebodyoftheeel，havethenatureofascolex。
　　Henceonemightsuppose，inconnexionwiththeoriginofmenandquadrupeds，that，ifevertheywerereally’earth—born’assomesay，theycameintobeinginoneoftwoways；thateitheritwasbytheformationofascolexatfirstorelseitwasoutofeggs。Foreithertheymusthavehadinthemselvesthenutrimentforgrowth（andsuchaconceptionisascolex）ortheymusthavegotitfromelsewhere，andthateitherfromthemotherorfrompartoftheconception。Ifthentheformerisimpossible（Imeanthatnourishmentshouldflowtothemfromtheearthasitdoesinanimalsfromthemother），thentheymusthavegotitfromsomepartoftheconception，andsuchgenerationwesayisfromanegg。
　　Itisplainthenthat，iftherereallywasanysuchbeginningofthegenerationofallanimals，itisreasonabletosupposetohavebeenoneofthesetwo，scolexoregg。Butitislessreasonabletosupposethatitwasfromeggs，forwedonotseesuchgenerationoccurringwithanyanimal，butwedoseetheotherbothinthesanguineaabovementionedandinthebloodlessanimals。Sucharesomeoftheinsectsandsucharethetestaceawhichwearediscussing；
　　fortheydonotdevelopoutofapartofsomething（asdoanimalsfromeggs），andtheygrowlikeascolex。Forthescolexgrowstowardstheupperpartandthefirstprinciple，sinceinthelowerpartisthenourishmentfortheupper。Andthisresemblesthedevelopmentofanimalsfromeggs，exceptthattheselatterconsumethewholeegg，whereasinthescolex，whentheupperparthasgrownbytakingupintoitselfpartofthesubstanceinthelowerpart，thelowerpartisthendifferentiatedoutoftherest。Thereasonisthatinlaterlifealsothenourishmentisabsorbedbyallanimalsinthepartbelowthehypozoma。
　　Thatthescolexgrowsinthiswayisplaininthecaseofbeesandthelike，foratfirstthelowerpartislargeinthemandtheupperissmaller。Thedetailsofgrowthinthetestaceaaresimilar。Thisisplaininthewhorlsoftheturbinata，foralwaysastheanimalgrowsthewhorlsbecomelargertowardsthefrontandwhatiscalledtheheadofthecreature。
　　Wehavenowprettywelldescribedthemannerofthedevelopmentoftheseandtheotherspontaneouslygeneratedanimals。Thatallthetestaceaareformedspontaneouslyisclearfromsuchfactsasthese。
　　Theycomeintobeingonthesideofboatswhenthefrothymudputrefies。Inmanyplaceswherepreviouslynothingofthekindexisted，theso—calledlimnostrea，akindofoyster，havecomeintobeingwhenthespotturnedmuddythroughwantofwater；thuswhenanavalarmamentcastanchoratRhodesanumberofclayvesselswerethrownoutintothesea，andaftersometime，whenmudhadcollectedroundthem，oystersusedtobefoundinthem。Hereisanotherproofthatsuchanimalsdonotemitanygenerativesubstancefromthemselves；whencertainChianscarriedsomeliveoystersoverfromPyrrhainLesbosandplacedtheminnarrowstraitsoftheseawheretidesclash，theybecamenomorenumerousastimepassed，butincreasedgreatlyinsize。Theso—calledeggscontributetogenerationbutareonlyacondition，likefatinthesanguinea，andthereforetheoystersaresavouryattheseperiods。Aproofthatthissubstanceisnotreallyeggsisthefactthatsuch’eggs’arealwaysfoundinsometestacea，asinpinnae，whelks，andpurple—fish；onlytheyaresometimeslargerandsometimessmaller；inothersaspectens，mussels，andtheso—calledlimnostrea，theyarenotalwayspresentbutonlyinthespring；astheseasonadvancestheydwindleandatlastdisappearaltogether；thereasonbeingthatthespringisfavourabletotheirbeingingoodcondition。Inothersagain，astheascidians，nothingofthesortisvisible。（Thedetailsconcerningtheselast，andtheplacesinwhichtheycomeintobeing，mustbelearntfromtheEnquiry。）
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　　WEhavethusspokenofthegenerationofanimalsbothgenerallyandseparatelyinallthedifferentclasses。But，sincemaleandfemalearedistinctinthemostperfectofthem，andsincewesaythatthesexesarefirstprinciplesofalllivingthingswhetheranimalsorplants，onlyinsomeofthemthesexesareseparatedandinothersnot，thereforewemustspeakfirstoftheoriginofthesexesinthelatter。Forwhiletheanimalisstillimperfectinitskindthedistinctionisalreadymadebetweenmaleandfemale。
　　Itisdisputed，however，whethertheembryoismaleorfemale，asthecasemaybe，evenbeforethedistinctionisplaintooursenses，andfurtherwhetheritisthusdifferentiatedwithinthemotherorevenearlier。Itissaidbysome，asbyAnaxagorasandotherofthephysicists，thatthisantithesisexistsfromthebeginninginthegermsorseeds；forthegerm，theysay，comesfromthemalewhilethefemaleonlyprovidestheplaceinwhichitistobedeveloped，andthemaleisfromtheright，thefemalefromthelefttestis，andsoalsothatthemaleembryoisintherightoftheuterus，thefemaleintheleft。Others，asEmpedocles，saythatthedifferentiationtakesplaceintheuterus；forhesaysthatiftheuterusishotorcoldwhatentersitbecomesmaleorfemale，thecauseoftheheatorcoldbeingtheflowofthecatamenia，accordingasitiscolderorhotter，more’antique’ormore’recent’。DemocritusofAbderaalsosaysthatthedifferentiationofsextakesplacewithinthemother；
　　thathoweveritisnotbecauseofheatandcoldthatoneembryobecomesfemaleandanothermale，butthatitdependsonthequestionwhichparentitiswhosesemenprevails，—notthewholeofthesemen，butthatwhichhascomefromthepartbywhichmaleandfemaledifferfromoneanother。Thisisabettertheory，forcertainlyEmpedocleshasmadearatherlight—heartedassumptioninthinkingthatthedifferencebetweenthemisdueonlytocoldandheat，whenhesawthattherewasagreatdifferenceinthewholeofthesexualparts，thedifferenceinfactbetweenthemalepudendaandtheuterus。
　　Forsupposetwoanimalsalreadymouldedinembryo，theonehavingallthepartsofthefemale，theotherthoseofthemale；supposethemthentobeputintotheuterusasintoanoven，theformerwhentheovenishot，thelatterwhenitiscold；thenontheviewofEmpedoclesthatwhichhasnouteruswillbefemaleandthatwhichhaswillbemale。Butthisisimpossible。ThusthetheoryofDemocrituswouldbethebetterofthetwo，atleastasfarasthisgoes，forheseeksfortheoriginofthisdifferenceandtriestosetitforth；whetherhedoessowellornotisanotherquestion。
　　Again，ifheatandcoldwerethecauseofthedifferenceoftheparts，thisoughttohavebeenstatedbythosewhomaintaintheviewofEmpedocles；fortoexplaintheoriginofmaleandfemaleispracticallythesamethingastoexplainthis，whichisthemanifestdifferencebetweenthem。Anditisnosmallmatter，startingfromtemperatureasaprinciple，tocollectthecauseoftheoriginoftheseparts，asifitwereanecessaryconsequenceforthispartwhichtheycalltheuterustobeformedintheembryoundertheinfluenceofcoldbutnotunderthatofheat。Thesameappliesalsotothepartswhichserveforintercourse，sincethesealsodifferinthewaystatedpreviously。
　　Moreovermaleandfemaletwinsareoftenfoundtogetherinthesamepartoftheuterus；thiswehaveobservedsufficientlybydissectioninallthevivipara，bothlandanimalsandfish。NowifEmpedocleshadnotseenthisitwasonlynaturalforhimtofallintoerrorinassigningthiscauseofhis；butifhehadseenititisstrangethatheshouldstillthinktheheatorcoldoftheuterustobethecause，sinceonhistheoryboththesetwinswouldhavebecomeeithermaleorfemale，butasitiswedonotseethistobethefact。
　　Againhesaysthatthepartsoftheembryoare’sundered’，somebeinginthemaleandsomeinthefemaleparent，whichiswhytheydesireintercoursewithoneanother。Ifsoitisnecessarythatthesexualpartsliketherestshouldbeseparatedfromoneanother，alreadyexistingasmassesofacertainsize，andthattheyshouldcomeintobeingintheembryoonaccountofunitingwithoneanother，notonaccountofcoolingorheatingofthesemen。ButperhapsitwouldtaketoolongtodiscussthoroughlysuchacauseasthiswhichisstatedbyEmpedocles，foritswholecharacterseemstobefanciful。If，however，thefactsaboutsemenaresuchaswehaveactuallystated，ifitdoesnotcomefromthewholeofthebodyofthemaleparentandifthesecretionofthemaledoesnotgiveanymaterialatalltotheembryo，thenwemustmakeastandagainstbothEmpedoclesandDemocritusandanyoneelsewhoarguesonthesamelines。Forthenitisnotpossiblethatthebodyoftheembryoshouldexist’sundered’，partinthefemaleparentandpartinthemale，asEmpedoclessaysinthewords：’Butthenatureofthelimbshathbeensundered，partintheman’s……’；noryetthatawholeembryoisdrawnofffromeachparentandthecombinationofthetwobecomesmaleorfemaleaccordingasonepartprevailsoveranother。
　　And，totakeamoregeneralview，thoughitisbettertosaythattheonepartmakestheembryofemalebyprevailingthroughsomesuperioritythantoassignnothingbutheatasthecausewithoutanyreflection，yet，astheformofthepudendumalsovariesalongwiththeuterusfromthatofthefather，weneedanexplanationofthefactthatboththesepartsgoalongwitheachother。Ifitisbecausetheyareneareachother，theneachoftheotherpartsalsooughttogowiththem，foroneoftheprevailingpartsisalwaysnearanotherpartwherethestruggleisnotyetdecided；thustheoffspringwouldbenotonlyfemaleormalebutalsolikeitsmotherorfatherrespectivelyinallotherdetails。
　　Besides，itisabsurdtosupposethatthesepartsshouldcomeintobeingassomethingisolated，withoutthebodyasawholehavingchangedalongwiththem。Takefirstandforemosttheblood—vessels，roundwhichthewholemassofthefleshliesasroundaframework。
　　Itisnotreasonablethattheseshouldbecomeofacertainqualitybecauseoftheuterus，butratherthattheuterusshoulddosoonaccountofthem。Forthoughitistruethateachisareceptacleofbloodofsomekind，stillthesystemofthevesselsispriortotheother；themovingprinciplemustneedsalwaysbepriortothatwhichitmoves，anditisbecauseitisitselfofacertainqualitythatitisthecauseofthedevelopment。Thedifference，then，ofthesepartsascomparedwitheachotherinthetwosexesisonlyaconcomitantresult；notthisbutsomethingelsemustbeheldtobethefirstprincipleandthecauseofthedevelopmentofanembryoasmaleorfemale；thisissoevenifnosemenissecretedbyeithermaleorfemale，buttheembryoisformedinanywayyouplease。
　　ThesameargumentasthatwithwhichwemeetEmpedoclesandDemocrituswillserveagainstthosewhosaythatthemalecomesfromtherightandthefemalefromtheleft。Ifthemalecontributesnomaterialtotheembryo，therecanbenothinginthisview。If，astheysay，hedoescontributesomethingofthesort，wemustconfronttheminthesamewayaswedidthetheoryofEmpedocles，whichaccountsforthedifferencebetweenmaleandfemalebytheheatandcoldoftheuterus。Theymakethesamemistakeashedoes，whentheyaccountforthedifferencebytheir’rightandleft’，thoughtheyseethatthesexesdifferactuallybythewholeofthesexualparts；forwhatreasonthenisthebodyoftheuterustoexistinthoseembryoswhichcomefromtheleftandnotinthosefromtheright？Forifanembryohavecomefromtheleftbuthasnotacquiredthispart，itwillbeafemalewithoutauterus，andsotoothereisnothingtostopanotherfrombeingamalewithauterus！Besidesashasbeensaidbefore，afemaleembryohasbeenobservedintherightpartoftheuterus，amaleintheleft，oragainbothatonceinthesamepart，andthisnotonlyoncebutseveraltimes。
　　Someagain，persuadedofthetruthofaviewresemblingthatofthesephilosophers，saythatifamancopulateswiththerightorlefttestistieduptheresultismaleorfemaleoffspringrespectively；soatleastLeophanesasserted。Andsomesaythatthesamehappensinthecaseofthosewhohaveoneorothertestisexcised，notspeakingtruthbutvaticinatingwhatwillhappenfromprobabilitiesandjumpingattheconclusionthatitissobeforeseeingthatitprovestobeso。
　　Moreover，theyknownotthatthesepartsofanimalscontributenothingtotheproductionofonesexratherthantheother；aproofofthisisthatmanyanimalsinwhichthedistinctionofsexexists，andwhichproducebothmaleandfemaleoffspring，neverthelesshavenotestes，asthefootlessanimals；Imeantheclassesoffishandofserpents。
　　Tosuppose，then，eitherthatheatandcoldarethecausesofmaleandfemale，orthatthedifferentsexescomefromtherightandleft，isnotaltogetherunreasonableinitself；fortherightofthebodyishotterthantheleft，andtheconcoctedsemenishotterthantheunconcocted；again，thethickenedisconcocted，andthemorethickenedismorefertile。Yettoputitinthiswayistoseekforthecausefromtooremoteastarting—point；wemustdrawneartheimmediatecausesinsofarasitispossibleforus。
　　Wehave，then，previouslyspokenelsewhereofboththebodyasawholeanditsparts，explainingwhateachpartisandforwhatreasonitexists。But（1）themaleandfemalearedistinguishedbyacertaincapacityandincapacity。（Forthemaleisthatwhichcanconcoctthebloodintosemenandwhichcanformandsecreteanddischargeasemencarryingwithittheprincipleofform—by’principle’Idonotmeanamaterialprincipleoutofwhichcomesintobeinganoffspringresemblingtheparent，butImeanthefirstmovingcause，whetherithavepowertoactassuchinthethingitselforinsomethingelse—butthefemaleisthatwhichreceivessemen，indeed，butcannotformitforitselforsecreteordischargeit。）
　　And（2）allconcoctionworksbymeansofheat。Thereforethemalesofanimalsmustneedsbehotterthanthefemales。Foritisbyreasonofcoldandincapacitythatthefemaleismoreabundantinbloodincertainpartsofheranatomy，andthisabundanceisanevidenceoftheexactoppositeofwhatsomesuppose，thinkingthatthefemaleishotterthanthemaleforthisreason，i。e。thedischargeofthecatamenia。Itistruethatbloodishot，andthatwhichhasmoreofitishotterthanthatwhichhasless。Buttheyassumethatthisdischargeoccursthroughexcessofbloodandofheat，asifitcouldbetakenforgrantedthatallbloodisequallybloodifonlyitbeliquidandsanguineousincolour，andasifitmightnotbecomelessinquantitybutpurerinqualityinthosewhoassimilatenourishmentproperly。Infacttheylookuponthisresidualdischargeinthesamelightasthatoftheintestines，whentheythinkthatagreateramountofitisasignofahotternature，whereasthetruthisjusttheopposite。Forconsidertheproductionoffruit；thenutrimentinitsfirststageisabundant，buttheusefulproductderivedfromitissmall，indeedthefinalresultisnothingatallcomparedtothequantityinthefirststage。Soisitwiththebody；
　　thevariouspartsreceiveandworkupthenutriment，fromthewholeofwhichthefinalresultisquitesmall。Thisisbloodinsomeanimals，insomeitsanalogue。Nowsince（1）theonesexisableandtheotherisunabletoreducetheresidualsecretiontoapureform，and（2）everycapacityorpowerinanorganismhasacertaincorrespondingorgan，whetherthefacultyproducesthedesiredresultsinalowerdegreeorinahigherdegree，andthetwosexescorrespondinthismanner（theterms’able’and’unable’beingusedinmoresensesthanone）—thereforeitisnecessarythatbothfemaleandmaleshouldhaveorgans。Accordinglytheonehastheuterus，theotherthemaleorgans。
　　Again，Naturegivesboththefacultyandtheorgantoeachindividualatthesametime，foritisbetterso。Henceeachregioncomesintobeingalongwiththesecretionsandthefaculties，ase。g。thefacultyofsightisnotperfectedwithouttheeye，northeeyewithoutthefacultyofsight；andsotootheintestineandbladdercomeintobeingalongwiththefacultyofformingtheexcreta。Andsincethatfromwhichanorgancomesintobeingandthatbywhichitisincreasedarethesame（i。e。thenutriment），eachofthepartswillbemadeoutofsuchamaterialandsuchresidualmatterasitisabletoreceive。Inthesecondplace，again，itisformed，aswesay，inacertainsense，outofitsopposite。Thirdly，wemustunderstandbesidesthisthat，ifitistruethatwhenathingperishesitbecomestheoppositeofwhatitwas，itisnecessaryalsothatwhatisnotundertheswayofthatwhichmadeitmustchangeintoitsopposite。Afterthesepremissesitwillperhapsbenowclearerforwhatreasononeembryobecomesfemaleandanothermale。Forwhenthefirstprincipledoesnotbearswayandcannotconcoctthenourishmentthroughlackofheatnorbringitintoitsproperform，butisdefeatedinthisrespect，thenmustneedsthematerialwhichitworksonchangeintoitsopposite。Nowthefemaleisoppositetothemale，andthatinsofarastheoneisfemaleandtheothermale。
　　Andsinceitdiffersinitsfaculty，itsorganalsoisdifferent，sothattheembryochangesintothisstate。Andasonepartoffirst—rateimportancechanges，thewholesystemoftheanimaldiffersgreatlyinformalongwithit。Thismaybeseeninthecaseofeunuchs，who，thoughmutilatedinonepartalone，departsomuchfromtheiroriginalappearanceandapproximatecloselytothefemaleform。Thereasonofthisisthatsomeofthepartsareprinciples，andwhenaprincipleismovedoraffectedneedsmustmanyofthepartsthatgoalongwithitchangewithit。
　　Ifthen（1）themalequalityoressenceisaprincipleandacause，and（2）themaleissuchinvirtueofacertaincapacityandthefemaleissuchinvirtueofanincapacity，and（3）theessenceordefinitionofthecapacityandoftheincapacityisabilityorinabilitytoconcoctthenourishmentinitsultimatestage，thisbeingcalledbloodinthesanguineaandtheanalogueofbloodintheotheranimals，and（4）thecauseofthiscapacityisinthefirstprincipleandinthepartwhichcontainstheprincipleofnaturalheat—thereforeaheartmustbeformedinthesanguinea（andtheresultinganimalwillbeeithermaleorfemale），andintheotherkindswhichpossessthesexesmustbeformedthatwhichisanalogoustotheheart。
　　This，then，isthefirstprincipleandcauseofmaleandfemale，andthisisthepartofthebodyinwhichitresides。Buttheanimalbecomesdefinitelyfemaleormalebythetimewhenitpossessesalsothepartsbywhichthefemalediffersfromthemale，foritisnotinvirtueofanypartyoupleasethatitismaleorfemale，anymorethanitisabletoseeorhearbypossessinganypartyouplease。
　　Torecapitulate，wesaythatthesemen，whichisthefoundationoftheembryo，istheultimatesecretionofthenutriment。ByultimateImeanthatwhichiscarriedtoeverypartofthebody，andthisisalsothereasonwhytheoffspringisliketheparent。Foritmakesnodifferencewhetherwesaythatthesemencomesfromallthepartsorgoestoallofthem，butthelatteristhebetter。Butthesemenofthemalediffersfromthecorrespondingsecretionofthefemaleinthatitcontainsaprinciplewithinitselfofsuchakindastosetupmovementsalsointheembryoandtoconcoctthoroughlytheultimatenourishment，whereasthesecretionofthefemalecontainsmaterialalone。If，then，themaleelementprevailsitdrawsthefemaleelementintoitself，butifitisprevailedoveritchangesintotheoppositeorisdestroyed。Butthefemaleisoppositetothemale，andisfemalebecauseofitsinabilitytoconcoctandofthecoldnessofthesanguineousnutriment。AndNatureassignstoeachofthesecretionsthepartfittedtoreceiveit。Butthesemenisasecretion，andthisinthehotteranimalswithblood，i。e。themales，ismoderateinquantity，whereforetherecipientpartsofthissecretioninmalesareonlypassages。Butthefemales，owingtoinabilitytoconcoct，haveagreatquantityofblood，foritcannotbeworkedupintosemen。Thereforetheymustalsohaveaparttoreceivethis，andthispartmustbeunlikethepassagesofthemaleandofaconsiderablesize。Thisiswhytheuterusisofsuchanature，thisbeingthepartbywhichthefemalediffersfromthemale。
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　　Wehavethusstatedforwhatreasontheonebecomesfemaleandtheothermale。Observedfactsconfirmwhatwehavesaid。Formorefemalesareproducedbytheyoungandbythosevergingonoldagethanbythoseintheprimeoflife；intheformerthevitalheatisnotyetperfect，inthelatteritisfailing。Andthoseofamoisterandmorefemininestateofbodyaremorewonttobegetfemales，andaliquidsemencausesthismorethanathicker；nowallthesecharacteristicscomeofdeficiencyinnaturalheat。
　　Again，moremalesarebornifcopulationtakesplacewhennorththanwhensouthwindsareblowing。Forinthelattercasetheanimalsproducemoresecretion，andtoomuchsecretionishardertoconcoct；
　　hencethesemenofthemalesismoreliquid，andsoisthedischargeofthecatamenia。
　　Alsothefactthatthecatameniaoccurinthecourseofnatureratherwhenthemonthiswaningisduetothesamecauses。Forthistimeofthemonthiscolderandmoisterbecauseofthewaningandfailureofthemoon；asthesunmakeswinterandsummerintheyearasawhole，sodoesthemooninthemonth。Thisisnotduetotheturningofthemoon，butitgrowswarmerasthelightincreasesandcolderasitwanes。
　　Theshepherdsalsosaythatitnotonlymakesadifferenceintheproductionofmalesandfemalesifcopulationtakesplaceduringnorthernorsoutherlywinds，buteveniftheanimalswhilecopulatinglooktowardsthesouthornorth；sosmallathingwillsometimesturnthescaleandcausecoldorheat，andtheseagaininfluencegeneration。
　　Themaleandfemale，then，aredistinguishedgenerally，ascomparedwithoneanotherinconnexionwiththeproductionofmaleandfemaleoffspring，forthecausesstated。However，theyalsoneedacertaincorrespondencewithoneanothertoproduceatall，forallthingsthatcomeintobeingasproductsofartorofNatureexistinvirtueofacertainratio。Nowifthehotpreponderatestoomuchitdriesuptheliquid；ifitisverydeficientitdoesnotsolidifyit；fortheartisticornaturalproductweneedtheduemeanbetweentheextremes。Otherwiseitwillbeasincooking；toomuchfireburnsthemeat，toolittledoesnotcookit，andineithercasetheprocessisafailure。Soalsothereisneedofdueproportioninthemixtureofthemaleandfemaleelements。Andforthiscauseitoftenhappenstomanyofbothsexesthattheydonotgeneratewithoneanother，butifdivorcedandremarriedtoothersdogenerate；andtheseoppositionsshowthemselvessometimesinyouth，sometimesinadvancedage，alikeasconcernsfertilityorinfertility，andasconcernsgenerationofmaleorfemaleoffspring。
　　Onecountryalsodiffersfromanotherintheserespects，andonewaterfromanother，forthesamereasons。Forthenourishmentandthemedicalconditionofthebodyareofsuchorsuchakindbecauseofthetemperingofthesurroundingairandofthefoodenteringthebody，especiallythewater；formenconsumemoreofthisthanofanythingelse，andthisentersasnourishmentintoallfood，evensolids。Hencehardwaterscauseinfertility，andcoldwatersthebirthoffemales。
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　　Thesamecausesmustbeheldresponsibleforthefollowinggroupsoffacts。（1）Somechildrenresembletheirparents，whileothersdonot；somebeinglikethefatherandotherslikethemother，bothinthebodyasawholeandineachpart，maleandfemaleoffspringresemblingfatherandmotherrespectivelyratherthantheotherwayabout。（2）Theyresembletheirparentsmorethanremoterancestors，andresemblethoseancestorsmorethananychanceindividual。（3）
　　Some，thoughresemblingnoneoftheirrelations，yetdoatanyrateresembleahumanbeing，butothersarenotevenlikeahumanbeingbutamonstrosity。Forevenhewhodoesnotresemblehisparentsisalreadyinacertainsenseamonstrosity；forinthesecasesNaturehasinawaydepartedfromthetype。Thefirstdepartureindeedisthattheoffspringshouldbecomefemaleinsteadofmale；this，however，isanaturalnecessity。（Fortheclassofanimalsdividedintosexesmustbepreserved，andasitispossibleforthemalesometimesnottoprevailoverthefemaleinthemixtureofthetwoelements，eitherthroughyouthorageorsomeothersuchcause，itisnecessarythatanimalsshouldproducefemaleyoung）。Andthemonstrosity，thoughnotnecessaryinregardofafinalcauseandanend，yetisnecessaryaccidentally。Asfortheoriginofit，wemustlookatitinthisway。Ifthegenerativesecretioninthecatameniaisproperlyconcocted，themovementimpartedbythemalewillmaketheformoftheembryointhelikenessofitself。（Whetherwesaythatitisthesemenorthismovementthatmakeseachofthepartsgrow，makesnodifference；noragainwhetherwesaythatit’makesthemgrow’or’formsthemfromthebeginning’，fortheformulaofthemovementisthesameineithercase。）Thusifthismovementprevail，itwillmaketheembryomaleandnotfemale，likethefatherandnotlikethemother；ifitprevailnot，theembryoisdeficientinthatfacultyinwhichithasnotprevailed。By’eachfaculty’Imeanthis。Thatwhichgeneratesisnotonlymalebutalsoaparticularmale，e。g。
　　CoriscusorSocrates，anditisnotonlyCoriscusbutalsoaman。Inthiswaysomeofthecharacteristicsofthefatheraremoreneartohim，othersmoreremotefromhimconsideredsimplyasaparentandnotinreferencetohisaccidentalqualities（asforinstanceiftheparentisascholarortheneighbourofsomeparticularperson）。
　　Nowthepeculiarandindividualhasalwaysmoreforceingenerationthanthemoregeneralandwidercharacteristics。Coriscusisbothamanandananimal，buthismanhoodisnearertohisindividualexistencethanishisanimalhood。Ingenerationboththeindividualandtheclassareoperative，buttheindividualisthemoresoofthetwo，forthisistheonlytrueexistence。Andtheoffspringisproducedindeedofacertainquality，butalsoasanindividual，andthislatteristhetrueexistence。Thereforeitisfromtheforcesofallsuchexistencesthattheefficientmovementscomewhichexistinthesemen；potentiallyfromremoterancestorsbutinahigherdegreeandmorenearlyfromtheindividual（andbytheindividualI
　　meane。g。CoriscusorSocrates）。Nowsinceeverythingchangesnotintoanythinghaphazardbutintoitsopposite，thereforealsothatwhichisnotprevailedoveringenerationmustchangeandbecometheopposite，inrespectofthatparticularforceinwhichthepaternalandefficientormovingelementhasnotprevailed。Ifthenithasnotprevailedinsofarasitismale，theoffspringbecomesfemale；
　　ifinsofarasitisCoriscusorSocrates，theoffspringdoesnotresemblethefatherbutthemother。Foras’father’and’mother’areopposedasgeneralterms，soalsotheindividualfatherisopposedtotheindividualmother。Thelikeappliesalsototheforcesthatcomenextinorder，fortheoffspringalwayschangesratherintothelikenessofthenearerancestorthanthemoreremote，bothinthepaternalandinthematernalline。
　　Someofthemovementsexistinthesemenactually，otherspotentially；actually，thoseofthefatherandthegeneraltype，asmanandanimal；potentiallythoseofthefemaleandtheremoterancestors。Thusthemaleandefficientprinciple，ifitloseitsownnature，changestoitsopposites，butthemovementswhichformtheembryochangeintothosenearlyconnectedwiththem；forinstance，ifthemovementofthemaleparentberesolved，itchangesbyaveryslightdifferenceintothatofhisfather，andinthenextinstanceintothatofhisgrandfather；andinthiswaynotonlyinthemalebutalsointhefemalelinethemovementofthefemaleparentchangesintothatofhermother，and，ifnotintothis，thenintothatofhergrandmother；andsimilarlyalsowiththemoreremoteancestors。
　　Naturallythenitismostlikelythatthecharacteristicsof’male’andoftheindividualfatherwillgotogether，whethertheyprevailorareprevailedover。Forthedifferencebetweenthemissmallsothatthereisnodifficultyinbothconcurring，forSocratesisanindividualmanwithcertaincharacters。Henceforthemostpartthemaleoffspringresemblethefather，andthefemalethemother。Forinthelattercasethelossofbothcharacterstakesplaceatonce，andthechangeisintothetwoopposites；nowisopposedtomale，andtheindividualmothertotheindividualfather。
　　ButifthemovementcomingfromthemaleprincipleprevailswhilethatcomingfromtheindividualSocratesdoesnot，orviceversa，thentheresultisthatmalechildrenareproducedresemblingthemotherandfemalechildrenresemblingthefather。
　　Ifagainthemovementsberesolved，ifthemalecharacterremainbutthemovementcomingfromtheindividualSocratesberesolvedintothatofthefatherofSocrates，theresultwillbeamalechildresemblingitsgrandfatherorsomeotherofitsmoreremoteancestorsinthemalelineonthesameprinciple。Ifthemaleprinciplebeprevailedover，thechildwillbefemaleandresemblingmostprobablyitsmother，but，ifthemovementcomingfromthemotheralsoberesolved，itwillresembleitsmother’smotherortheresemblancewillbetosomeotherofitsmoreremoteancestorsinthefemalelineonthesameprinciple。
　　Thesameappliesalsototheseparateparts，foroftensomeofthesetakeafterthefather，andothersafterthemother，andyetothersaftersomeoftheremoterancestors。For，ashasbeenoftensaidalready，someofthemovementswhichformthepartsexistinthesemenactuallyandotherspotentially。Wemustgraspcertainfundamentalgeneralprinciples，notonlythatjustmentioned（thatsomeofthemovementsexistpotentiallyandothersactually），butalsotwoothers，thatifacharacterbeprevailedoveritchangesintoitsopposite，and，ifitberesolved，isresolvedintothemovementnextalliedtoit—ifless，intothatwhichisnear，ifmore，intothatwhichisfurtherremoved。Finally，themovementsaresoconfusedtogetherthatthereisnoresemblancetoanyofthefamilyorkindred，buttheonlycharacterthatremainsisthatcommontotherace，i。e。
　　itisahumanbeing。Thereasonofthisisthatthisiscloselyknitupwiththeindividualcharacteristics；’humanbeing’isthegeneralterm，whileSocrates，thefather，andthemother，whoevershemaybe，areindividuals。
　　Thereasonwhythemovementsareresolvedisthis。Theagentisitselfacteduponbythatonwhichitacts；thusthatwhichcutsisbluntedbythatwhichiscutbyit，thatwhichheatsiscooledbythatwhichisheatedbyit，andingeneralthemovingorefficientcause（exceptinthecaseofthefirstcauseofall）doesitselfreceivesomemotioninreturn；e。g。whatpushesisitselfinawaypushedagainandwhatcrushesisitselfcrushedagain。Sometimesitisaltogethermoreacteduponthanisthethingonwhichitacts，sothatwhatisheatingorcoolingsomethingelseisitselfcooledorheated；sometimeshavingproducednoeffect，sometimeslessthanithasitselfreceived。（Thisquestionhasbeentreatedinthespecialdiscussionofactionandreaction，whereitislaiddowninwhatclassesofthingsactionandreactionexist。）Nowthatwhichisactedonescapesandisnotmasteredbythesemen，eitherthroughdeficiencyofpowerintheconcoctingandmovingagentorbecausewhatshouldbeconcoctedandformedintodistinctpartsistoocoldandintoogreatquantity。Thusthemovingagent，masteringitinonepartbutnotinanother，makestheembryoinformationtobemultiform，ashappenswithathletesbecausetheyeatsomuch。Forowingtothequantityoftheirfoodtheirnatureisnotabletomasteritall，soastoincreaseandarrangetheirformsymmetrically；thereforetheirlimbsdevelopirregularly，sometimesindeedalmostsomuchthatnooneofthemresembleswhatitwasbefore。Similartothisisalsothediseaseknownassatyrism，inwhichthefaceappearslikethatofasatyrowingtoaquantityofunconcoctedhumourorwindbeingdivertedintopartsoftheface。
　　Wehavethusdiscussedthecauseofallthesephenomena，（1）
　　femaleandmaleoffspringareproduced，（2）whysomearesimilartotheirparents，femaletofemaleandmaletomale，andotherstheotherwayabout，femalesbeingsimilartothefatherandmalestothemother，andingeneralwhysomeareliketheirancestorswhileothersarelikenoneofthem，andallthisasconcernsboththebodyasawholeandeachofthepartsseparately。Differentaccounts，however，havebeengivenofthesephenomenabysomeofthenature—philosophers；Imeanwhychildrenarelikeorunliketheirparents。Theygivetwoversionsofthereason。Somesaythatthechildismorelikethatparentofthetwofromwhomcomesmoresemen，thisapplyingequallybothtothebodyasawholeandtotheseparateparts，ontheassumptionthatsemencomesfromeachpartofbothparents；ifanequalpartcomesfromeach，then，theysay，thechildislikeneither。Butifthisisfalse，ifsemendoesnotcomeofffromthewholebodyoftheparents，itisclearthatthereasonassignedcannotbethecauseoflikenessandunlikeness。Moreover，theyarehardputtoittoexplainhowitisthatafemalechildcanbelikethefatherandamalelikethemother。For（1）thosewhoassignthesamecauseofsexasEmpedoclesorDemocritussaywhatisonothergroundsimpossible，and（2）thosewhosaythatitisdeterminedbythegreaterorsmalleramountofsemencomingthemaleorfemaleparent，andthatthisiswhyonechildismaleandanotherfemale，cannotshowhowthefemaleistoresemblethefatherandthemalethemother，foritisimpossiblethatmoreshouldcomefrombothatonce。Again，forwhatreasonisachildgenerallylikeitsancestors，eventhemoreremote？Noneofthesemenhascomefromthematanyrate。
　　Butthosewhoaccountforthesimilarityinthemannerwhichremainstobediscussed，explainthispointbetter，aswellastheothers。Fortherearesomewhosaythatthesemen，thoughone，isasitwereacommonmixture（panspermia）ofmanyelements；justas，ifoneshouldmixmanyjuicesinoneliquidandthentakesomefromit，itwouldbepossibletotake，notanequalquantityalwaysfromeachjuice，butsometimesmoreofoneandsometimesmoreofanother，sometimessomeofoneandnoneatallofanother，sotheysayitiswiththegenerativefluid，whichisamixtureofmanyelements，fortheoffspringresemblesthatparentfromwhichithasderivedmost。Thoughthistheoryisobscureandinmanywaysfictitious，itaimsatwhatisbetterexpressedbysayingthatwhatiscalled’panspermia’existspotentially，notactually；itcannotexistactually，butitcandosopotentially。Also，ifweassignonlyonesortofcause，itisnoteasytoexplainallthephenomena，（1）thedistinctionofsex，（2）whythefemaleisoftenlikethefatherandthemalelikethemother，andagain（3）theresemblancetoremoterancestors，andfurther（4）
　　thereasonwhytheoffspringissometimesunlikeanyofthesebutstillahumanbeing，butsometimes，（5）proceedingfurtherontheselines，appearsfinallytobenotevenahumanbeingbutonlysomekindofanimal，whatiscalledamonstrosity。
　　For，followingwhathasbeensaid，itremainstogivethereasonforsuchmonsters。Ifthemovementsimpartedbythesemenareresolvedandthematerialcontributedbythemotherisnotcontrolledbythem，atlastthereremainsthemostgeneralsubstratum，thatistosaytheanimal。Thenpeoplesaythatthechildhastheheadofaramorabull，andsoonwithotheranimals，asthatacalfhastheheadofachildorasheepthatofanox。Allthesemonstersresultfromthecausesstatedabove，buttheyarenoneofthethingstheyaresaidtobe；thereisonlysomesimilarity，suchasmayariseevenwherethereisnodefectofgrowth。Henceoftenjesterscomparesomeonewhoisnotbeautifultoa’goatbreathingfire’，oragaintoa’rambutting’，andacertainphysiognomistreducedallfacestothoseoftwoorthreeanimals，andhisargumentsoftenprevailedonpeople。
　　That，however，itisimpossibleforsuchamonstrositytocomeintoexistence—Imeanoneanimalinanother—isshownbythegreatdifferenceintheperiodofgestationbetweenman，sheep，dog，andox，itbeingimpossibleforeachtobedevelopedexceptinitspropertime。
　　Thisisthedescriptionofsomeofthemonsterstalkedabout；othersaresuchbecausecertainpartsoftheirformaremultipliedsothattheyarebornwithmanyfeetormanyheads。
　　Theaccountofthecauseofmonstrositiesisverycloseandsimilarinawaytothatofthecauseofanimalsbeingborndefectiveinanypart，formonstrosityisalsoakindofdeficiency。
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　　Democritussaidthatmonstrositiesarosebecausetwoemissionsofseminalfluidmettogether，theonesucceedingtheotheratanintervaloftime；thatthelaterenteringintotheuterusreinforcedtheearliersothatthepartsoftheembryogrowtogetherandgetconfusedwithoneanother。Butinbirds，hesays，sincecopulationtakesplacequickly，boththeeggsandtheircolouralwayscrossoneanother。Butifitisthefact，asitmanifestlyis，thatseveralyoungareproducedfromoneemissionofsemenandasingleactofintercourse，itisbetternottodeserttheshortroadtogoalongwayabout，forinsuchcasesitisabsolutelynecessarythatthisshouldoccurwhenthesemenisnotseparatedbutallentersthefemaleatonce。
　　If，then，wemustattributethecausetothesemenofthemale，thiswillbethewayweshallhavetostateit，butwemustratherbyallmeanssupposethatthecauseliesinthematerialcontributedbythefemaleandintheembryoasitisforming。Hencealsosuchmonstrositiesappearveryrarelyinanimalsproducingonlyoneyoungone，morefrequentlyinthoseproducingmany，mostofallinbirdsandamongbirdsinthecommonfowl。Forthisbirdproducesmanyyoung，notonlybecauseitlaysoftenlikethepigeonfamily，butalsobecauseithasmanyembryosatonceandcopulatesalltheyearround。Thereforeitproducesmanydoubleeggs，fortheembryosgrowtogetherbecausetheyarenearoneanother，asoftenhappenswithmanyfruits。Insuchdoubleeggs，whentheyolksareseparatedbythemembrane，twoseparatechickensareproducedwithnothingabnormalaboutthem；
　　whentheyolksarecontinuous，withnodivisionbetweenthem，thechickensproducedaremonstrous，havingonebodyandheadbutfourlegsandfourwings；thisisbecausetheupperpartsareformedearlierfromthewhite，theirnourishmentbeingdrawnfromtheyolk，whereasthelowerpartcomesintobeinglateranditsnourishmentisoneandindivisible。
　　Asnakehasalsobeenobservedwithtwoheadsforthesamereason，thisclassalsobeingoviparousandproducingmanyyoung。
　　Monstrosities，however，arerareramongthemowingtotheshapeoftheuterus，forbyreasonofitslengththenumerouseggsaresetinaline。
　　Nothingofthekindoccurswithbeesandwasps，becausetheirbroodisinseparatecells。Butinthefowltheoppositeisthecase，wherebyitisplainthatwemustholdthecauseofsuchphenomenatolieinthematerial。So，too，monstrositiesarecommonerinotheranimalsiftheyproducemanyyoung。Hencetheyarelesscommoninman，forheproducesforthemostpartonlyoneyoungoneandthatperfect；eveninmanmonstrositiesoccurmoreofteninregionswherethewomengivebirthtomorethanoneatatime，asinEgypt。Andtheyarecommonerinsheepandgoats，sincetheyproducemoreyoung。Stillmoredoesthisapplytothefissipeds，forsuchanimalsproducemanyyoungandimperfect，asthedog，theyoungofthesecreaturesbeinggenerallyblind。Whythishappensandwhytheyproducemanyyoungmustbestatedlater，butinthemNaturehasmadeanadvancetowardstheproductionofmonstrositiesinthatwhattheygenerate，beingimperfect，issofarunliketheparent；nowmonstrositiesalsobelongtotheclassofthingsunliketheparent。
　　Thereforethisaccidentalsoofteninvadesanimalsofsuchanature。
　　So，too，itisinthesethattheso—called’metachoera’aremostfrequent，andtheconditionofthesealsoisinawaymonstrous，sincebothdeficiencyandexcessaremonstrous。ForthemonstrositybelongstotheclassofthingscontrarytoNature，notanyandeverykindofNature，butNatureinherusualoperations；nothingcanhappencontrarytoNatureconsideredaseternalandnecessary，butwespeakofthingsbeingcontrarytoherinthosecaseswherethingsgenerallyhappeninacertainwaybutmayalsohappeninanotherway。Infact，eveninthecaseofmonstrosities，wheneverthingsoccurcontraryindeedtotheestablishedorderbutstillalwaysinacertainwayandnotatrandom，theresultseemstobelessofamonstrositybecauseeventhatwhichiscontrarytoNatureisinacertainsenseaccordingtoNature，whenever，thatis，theformalnaturehasnotmasteredthematerialnature。Thereforetheydonotcallsuchthingsmonstrositiesanymorethanintheothercaseswhereaphenomenonoccurshabitually，asinfruits；forinstance，thereisavinewhichsomecall’capneos’；ifthisbearblackgrapestheydonotjudgeitamonstrositybecauseitisinthehabitofdoingthisveryoften。Thereasonisthatitisinitsnatureintermediatebetweenwhiteandblack；thusthechangeisnotaviolentonenor，sotosay，contrarytoNature；atleast，isitnotachangeintoanothernature。Butinanimalsproducingmanyyoungnotonlydothesamephenomenaoccur，butalsothenumerousembryoshinderoneanotherfrombecomingperfectandinterferewiththegenerativemotionsimpartedbythesemen。
　　Adifficultymayberaisedconcerning（1）theproductionofmanyyoungandthemultiplicationofthepartsinasingleyoungone，and（2）theproductionoffewyoungoronlyoneandthedeficiencyoftheparts。Sometimesanimalsarebornwithtoomanytoes，sometimeswithonealone，andsoonwiththeotherparts，fortheymaybemultipliedortheymaybeabsent。Again，theymayhavethegenerativepartsdoubled，theonebeingmale，theotherfemale；thisisknowninmenandespeciallyingoats。Forwhatarecalled’tragaenae’aresuchbecausetheyhavebothmaleandfemalegenerativeparts；thereisacasealsoofagoatbeingbornwithahornuponitsleg。Changesanddeficienciesarefoundalsointheinternalparts，animalseithernotpossessingsomeatall，orpossessingtheminarudimentarycondition，ortoonumerousorinthewrongplace。
　　Noanimal，indeed，haseverbeenbornwithoutaheart，buttheyarebornwithoutaspleenorwithtwospleensorwithonekidney；thereisnocaseagainoftotalabsenceoftheliver，buttherearecasesofitsbeingincomplete。Andallthesephenomenahavebeenseeninanimalsperfectandalive。Animalsalsowhichnaturallyhaveagall—bladderarefoundwithoutone；othersarefoundtohavemorethanone。Casesareknown，too，oftheorganschangingplaces，theliverbeingontheleft，thespleenontheright。Thesephenomenahavebeenobserved，asstatedabove，inanimalswhosegrowthisperfected；atthetimeofbirthgreatconfusionofeverykindhasbeenfound。ThosedeficiencywhichonlydepartalittlefromNaturecommonlylive；notsothosewhichdepartfurther，whentheunnaturalconditionisinthepartswhicharesovereignoverlife。
　　Thequestionthenaboutallthesecasesisthis。Arewetosupposethatasinglecauseisresponsiblefortheproductionofasingleyoungoneandforthedeficiencyoftheparts，andanotherbutstillasinglecausefortheproductionofmanyyoungandthemultiplicationofparts，ornot？
　　Inthefirstplaceitseemsonlyreasonabletowonderwhysomeanimalsproducemanyyoung，othersonlyone。Foritisthelargestanimalsthatproduceone，e。g。theelephant，camel，horse，andtheothersolid—hoofedungulates；ofthesesomearelargerthanallotheranimals，whiletheothersareofaremarkablesize。Butthedog，thewolf，andpracticallyallthefissipeds，producemany，eventhesmallmembersoftheclass，asthemousefamily。Thecloven—footedanimalsagainproducefew，exceptthepig，whichbelongstothosethatproducemany。Thiscertainlyseemssurprising，forweshouldexpectthelargeanimalstobeabletogeneratemoreyoungandtosecretemoresemen。Butpreciselywhatwewonderatisthereasonfornotwondering；itisjustbecauseoftheirsizethattheydonotproducemanyyoung，forthenutrimentisexpendedinsuchanimalsuponincreasingthebody。ButinthesmalleranimalsNaturetakesawayfromthesizeandaddstheexcesssogainedtotheseminalsecretion。