Aristotle 35 



Aristotle never ceased to take an interest, and among the 

 methods by which he sought to solve it was embryological 

 investigation. In his ideas on the methods of reproduction 

 we must seek also the main bases of such classification of 

 animals as he exhibits. His most important embryological 

 researches were made upon the chick. He asserts that the first 

 signs of development are noticeable on the third day, the heart 

 being visible as a palpitating blood-spot whence, as it develops, 

 two meandering blood-vessels extend to the surrounding tunics. 



( Generation from the egg', he says, ' proceeds in an identical 

 manner with all birds. . . . With the common hen after three 

 days and nights there is the first indication of the embryo. . . . 

 The heart appears like a speck of blood in the white of the egg. 

 This point beats and moves as though endowed with life, and 

 from it two vessels with blood in them trend in a convoluted 

 course . . . and a membrane carrying bloody fibres now envelops 

 the yolk, leading off from the vessels.' 1 



Aristotle lays considerable stress on the early appearance of 

 the heart in the embryo. Corresponding to the general 

 gradational view that he had formed of Nature, he held that 

 the most primitive and fundamentally important organs make 

 their appearance before the others. Among the organs all 

 give place to the heart, which he considered ' the first to live 

 and the last to die'. 2 



A little later he observed that the body had become dis- 

 tinguishable, and was at first very small and white. 



' The head is clearly distinguished and in it the eyes, swollen 

 out to a great extent. ... At the outset the under portion of the 

 body appears insignificant in comparison with the upper 

 portion. . . . 



' When an egg is ten days old the chick and all its parts are 



1 Historia animalium, vi. 3 ; 561*4. 



2 Cor prinmm movens itltimum moriens. This famous sentence is the 

 sense though not the phrasing of De generatione animalium, ii. i and 4. 



C 2 



