GENERATION OF ANIMALS, II. i. 



puzzle." How, we ask, is any plant formed out of the embryo 

 seed, or any animal out of the semen ? That which 

 is formed by means of a process must of necessity be 

 formed (a) out of something (b) by something (c) into 

 something. " Out of something." This of course 

 is the material or matter. Some animals have then- 

 primary matter ^ within themselves, having derived 

 it from the female parent, e.g., those animals which 

 are produced not viWparously but out of larvae 

 or eggs. Others derive it from the mother for a 

 considerable time by being suckled. These are the 

 animals which are produced \iviparously not exter- 

 nally only but also internally.*^ So then, that " out 

 of which " the parts are formed is material of this 

 sort. The problem now before us however is not 

 Out of what, but. By what, are they formed ? Either 

 something external fashions them, or else something 

 present in the semen or seminal fluid ; and this is 

 either some part of Soul, or Soul, or something which 

 possesses Soul. Now it would appear unreasonable 

 to suppose that anything external fashions all the 

 indi\idiial parts, whether they be the viscera or any 

 others, because unless it is in contact ** it cannot 

 set up any movement, and unless it sets up a 

 movement no effect can be produced upon any- 

 thing by it. Hence it follows that there must 

 be something already present inside the fetation 

 itself, which is either a part of it or separate from it. 



Meyer's The Rise of Embryology. Like many erroneous 

 theories, preformationism contained some truth, for we 

 know to-day that the course of the embryo's development 

 is predetermined by its genetic constitution. 



" Cf. 729 a 33 note. 



* This excludes the Selachia. 



" Cf. Bk. 1. 730 b 5 ff., and see App. B § 22, n. 



145 



