CHANGES IN THE EGG. 93 



about the navel, and increases with such ra- 

 pidity, that it covers nearly the whole inner 

 surface of the shell during the latter half of 



fold manner, with the chick : to the small intestines by a tube, 

 and by bloodvessels with the mesenteric artery and the venae 

 portae. During incubation, the yolk becomes thinner and paler, 

 by the admission of the inner white. At the same time, numer- 

 ous fringe-like vessels form on the inner surface of the yolk-bag ; 

 they absorb the yolk, and convey it into the veins of the yolk- 

 bag, giving nourishment to the chick. Thus, in the chick just 

 hatched, there is only a remainder of the yolk and its bag to be 

 found in the abdomen. These are completely removed in a few 

 days, leaving only a trace of its former existence in a scar on 

 the surface of the intestine. 



It is the generally received opinion that the blood in the em- 

 bryo chick is decarbonized by its contact with the oxygen of the 

 atmosphere, and yet it would appear, from a series of experi- 

 ments detailed in the Medical Reports of Guy's Hospital, London, 

 that the natural development of the contained embryo goes for- 

 ward, and is perfected, without the transmission of atmospheric 

 air to arterialize the venous circulation. 



The lining membrane of the shell, through which the air is 

 supposed to pass before reaching the chorion, was observed to 

 increase in density, and become apparently less permeable to 

 air in a ratio corresponding to the extent of time during which 

 the process of incubation had gone forward : a condition directly 

 opposed to that which might have been expected to obtain, as- 

 suming the correctness of the above-mentioned theory of decar- 

 bonization. It then occurred to the author of these experiments 

 that, in the cases in which it had been found that incubation did 

 not go forward when a barrier was put to the supposed egress 

 of atmospheric air, that a source of fallacy might have been pres- 

 ent, in the employment of a substance to protect the shell, which, 

 from its noxious qualities, had been fatal to the existence of the 



