22 ARISTOTLE AS A BIOLOGIST 



him to record this peculiarity in its relation to their many 

 differences of structure and reproductive habit. I used 

 to think of this phenomenon as one that Aristotle might 

 have learned from the fishermen, but, after a more careful 

 study of Johannes Miiller's book, I am convinced that this 

 is not the case. It was a discovery that could only have 

 been made by a skilled and learned anatomist. 



In a lengthy and beautiful account Aristotle describes 

 the development of the chick. It is on the third day 

 that the embryo becomes sufficiently formed for the 

 modern student to begin its study, and it was after just 

 three days (a little earlier, as Aristotle notes, in little 

 birds, a little later in larger ones) that Aristotle saw the 

 first clear indication of the embryo. Like a speck of 

 blood, he saw the heart beating, and its two umbilical 

 blood-vessels breaking out over the yolk. A little later 

 he saw the whole form of the body, noting the dispropor- 

 tionate size of head and eyes, and found the two sets of 

 blood-vessels leading, the one to the yolk-sac, the other to 

 the new-formed allantois. In the tiny chick of the tenth 

 day, he saw the stomach and other viscera ; he noted the 

 altered position of the heart and great blood-vessels ; he 

 traced clearly and fully the surrounding membranes ; he 

 opened the little eye to seek, but failed to find, the lens. 

 And at length he describes in detail the appearance and 

 attitude of the little chick, the absorption of the yolk, the 

 shrivelling of the membranes, just at the time when the 

 little bird begins to chip the shell, and before it steps out 

 into the world. While this epitome contains but a part 

 of what Aristotle saw (and without a lens it would be 

 hard to see more than he), it includes the notable fact of 

 the early appearance of the heart, the punctum saliens of 

 later writers, whose precedence of all other organs was 

 a chief reason for Aristotle's attributing to it a common, 



