62 EMBRYOLOGY IN ANTIQUITY [pt. ii 



The nature of semen receives a long discussion; it is decided at last 

 that it is a true secretion, and not a homogeneous natural part (a 

 tissue) nor a heterogeneous natural part (an organ) nor an unnatural 

 part such as a growth, nor mere nutriment, nor yet a waste product. 

 It is here that the theory is put forward that the semen supplies the 

 "form" to the embryo and whatever the female produces supplies 

 the matter fit for shaping. The obvious question has next to be 

 answered, what is it that the female supplies? Aristotle concludes 

 in chapters 19 and 20 that the female does not produce any semen, 

 as earlier philosophers had held, but that the menstrual blood is the 

 material from which the seminal fluid, in giving to it a form, will 

 cause the complete embryo to be produced. This was not a new idea, 

 but had already been suggested by the author of the Hippocratic 

 ire pi yovi]^. What was quite new here, was the idea that the semen 

 supplied or determined nothing but the form. Chapters 21 and 22 

 are rather confused ; they contain more arguments against pangenesis, 

 and considerations upon the contrast between the active nature of 

 the male and the passive nature of the female. Chapter 23, which 

 closes the first book, compares animals to divided plants, for plants 

 in Aristotle's view fertilise themselves. 



Book II opens with a magnificent chapter on the embryological 

 classification of animals, showing Aristotle, the systematist, at his 

 best — his classification is reproduced in Chart I. But the chapter 

 also includes a brilliant discussion of epigenesis or preformation, 

 fresh development or simple unfolding of pre-existent structures, 

 an antithesis which Aristotle was the first to perceive, and the sub- 

 sequent history of which is almost synonymous with the history of 

 embryology. The question in its acutest form was not settled until 

 the eighteenth century, but since then it has become clear that 

 there were elements of truth in the opinion which was the less true 

 of the two. Chapter 2 is not so important, though it has some 

 interesting chemical analogies; it compares semen to a foam, and 

 suggests that it was this foam, like that of the sea, which gave 

 birth to the goddess Aphrodite^. But chapter 3 returns to the 

 high level of speculation and thought found in the opening part of 

 the book, for it deals with the degree of aliveness which the embryo 

 has during its passage through its developmental stages. Aristotle 



^ To the Greeks all natural foams possessed a generative virtue, and a Zeus Aphrios 

 was worshipped at Pherae in Thrace. 



