GENERATION AND DEVELOPMENT. 207 



about the embryo itself, and separates it from the fluid.* 

 He seems to mean that the embryo is separated from the 

 remains of the white of the egg by the amnion ; it is not 

 evident, from his description, that he was aware that the 

 amnion encloses fluid which bathes the embryo. 



He next passes on to about the twentieth day, when the 

 chick, he says, chirps when the egg is disturbed. The head 

 of the chick, he says, is over the right leg, and its wing is 

 over the head. This is sufficiently accurate to show that 

 he carefully examined the position of the chick about the 

 twentieth day, for, at that time, the beak may be seen 

 pushed under the right wing, while the right claw rests 

 almost against the head. He also refers to the allantois, be 

 neath the shell membrane, about the twentieth day, and again 

 mentions the yolk sac. He compares them with the chorion, 

 or foetal membrane, in mammals, and states correctly that 

 the allantois falls away, while the yolk within the yolk sac 

 is withdrawn into the body of the chick. 



Referring to the pigeon, Aristotle says that on the day 

 before the young one is hatched, the egg is damaged or 

 perforated,! but it is not clear whether he believed that the 

 young one or the old ones did this. Albertus Magnus, who 

 seems to be translating a version of the above passage, clearly 

 states that the young pigeon breaks a piece out of the shell 

 with its bill. His translation, given by Aldrovandi,J reads : 

 &quot; In fissura ovi primo Columba parvula in eo existcns, pene- 

 trat testam anterior e parte rostri sui, ita ut testa elevetur ad 

 magnitudinem grani tritici, et postea dividit earn in duas 

 paries, et exit pulhis.&quot; 



- H. A. vi. c. 3, ss. 3-5. f II. A. vi. c. 4, s. 2. 



\ Ornithologia, vol. ii. 1610, Frankfurt, p. 184, first column. 



