282 EVOLUTION IN BIOLOGY. 



by epigenesiS) or successive differentiation of a rela- 

 tively homogeneous rudiment into the parts and struct- 

 ures which are characteristic of the adult. 



" Et primd, quidem, quoniam per epigenesin sive partium super- 

 exorientiura additamentum pullum fabricari certum est: quaenam 

 pars ante alias omnes exstruatur, et quid de ilia ejusque generandi 

 raodo observandum veniat, dispiciemus. Katum sane est et in ovo 

 manifest^ apparet quod Aristoteles de perfectorum animalium gene- 

 ratione enuntiat : nimirum, non omnes partes simul fieri, sed ordine 

 aliara post aliam; primumque existere particulam genitalem, cujus 

 virtute postea (tanquam ex principio quodam) reliquso omnes partes 

 prosiliant. Qualem in plantarum seminibus (fabis, puta, aut glan- 

 dibus) gemmam sive apicem protuberantem cerniinus, totius future 

 arboris principium. Estque hcec particula velut filius emancipate 

 seorsumque collocatus, et principium per se vivens ; unde postea 

 membrorum ordo describitur ; et qucecunque ad alwlvendum animal 

 pertinent, dispommtur* Quoniam enirn nulla pars se ipsam gene- 

 rat ; sed postquam gcnerata est, se ipsam jam auget ; ideo earn pri- 

 mtim oriri necesse est, qua principium augendi contineat (sive enim 

 planta, sive animal est, ceque omnibus inest quod mm Jidbeat vege- 

 tandi, sive nutriendi)^ simulque reliqaas omnes partes sno qnamque 

 ordine distinguat et formet ; proindeque in eadem primogenita par- 

 ticula anima priinario inest, sensus, motusque, et totius vitae auctor 

 et principium." (Exercitatio 51.) 



Harvey proceeds to contrast this view with that of 

 the " Medici," or followers of Hippocrates and Galen, 

 who, " badly philosophising," imagined that the brain, 

 the heart, and the liver were simultaneously first gene- 

 rated in the form of vesicles ; and, at the same time, 

 while expressing his agreement with Aristotle in the 

 principle of epigenesis, he maintains that it is the blood 

 which is the primal generative part, and not, as Aristotle 

 thought, the heart. 



* " De Gencratione Animalium," lib. ii. cap. x. 

 f " De Gcneratione," lib. ii. cap. iv. 



