Aristotle's biology 



the womb, and as living in a fuller sense (or 

 with more kinds of life) than could be ascribed 

 to an egg. In the three lower orders of blooded 

 animals, the young developed from an egg; 

 hence these were essentially oviparous, although 

 the egg might hatch within the mother and 

 the young come forth alive, as is the case of 

 certain sharks. Such animals were externally 

 viviparous, yet the young began as an egg 

 and not as a living foetus. 



In the grounds of this classification there 

 was fundamental error, arising from Aristotle's 

 ignorance of the mammalian egg, and yet much 

 penetrating observation, the results of which 

 still hold. His work upon the chick of the 

 domestic fowl, and his extraordinary anticipa- 

 tory description of the gestation of certain 

 sharks are examples. In his method of close 

 continuous study of the chick developing with- 

 in the egg, he may have been preceded by the 

 writer of one of the Hippocratic tracts. 32 



" Generation from the egg proceeds in an 

 identical manner with all birds, but the full 

 periods from conception to birth differ. . . . 

 With the common hen, after three days and 

 three nights, there is the first indication of the 

 embryo ... the heart appears like a speck of 



[55] 



