ON GENERATION. 295 



efficient cause of generation than the female, but some mixture 

 of the two; and that neither the menstrual blood nor its purest 

 part is the prime matter of the conception, but the spermatic 

 fluid; whence the first particles or their rudiments are spoken 

 of as spermatic, these at an after period being nourished and 

 made to increase through the blood. 



But it is obvious that neither is the egg engendered by the 

 cock and hen in this way; for the hen in the act of intercourse 

 emits no semen from which an egg might be formed ; nor can 

 aught like a seminal fluid of the hen be demonstrated at any 

 time ; and indeed the animal is destitute of the organs essential 

 to its preparation, the testes and vasa spermatica. And though 

 the hen have an effective force in common with the cock (as 

 must be manifest from what precedes), and it is a mixture of 

 some sort that renders an egg fruitful, still this does not happen 

 according to the predominance of the genitures, or the manner 

 of their mixture, for it is certain, and Fabricius admits it, that 

 the semen of the cock does not reach the cavity of the uterus ; 

 neither is there any trace of the egg to be discovered in the 

 uterus immediately after intercourse, and as its consequence, 

 although Aristotle himself repeatedly avers that there is, as- 

 serting that " something of the conception forthwith ensues." 

 But I shall by and by demonstrate that neither does any such 

 imaginary mixture of seminal fluids take place in any animal, 

 nor that immediately upon intercourse, even of a fruitful kind, 

 is there anything in the shape of semen or blood, or of the 

 rudiments of an embryo present or demonstrable in the cavity 

 of the uterus. Nothing is found in the egg or embryo which 

 leads us to suppose that the semen masculiuum is either there 

 contained or mingled. The vulgar notion of the chalazse being 

 the tread of the cock is a sheer mistake ; and I am surprised, 

 since there are two of them, one in either end of the egg, that 

 no one has yet been found to maintain that this was the cock's 

 seed, that the hen's. But this popular error is at once answered 

 by the fact that the chalazae are present with the same characters 

 in every egg, whether it be fertile or barren. 



