ANNALh 



OF 



PHILOSOPHY. 



JULY, 1821. 



Article I. 



A Memoir on the Physiology of the Egg, read before the Li/mean 

 Society of London, on March 21, 1809; an Abstract of which 

 is published in the Society's Transactions. By John Ayrton 

 Paris, MD. &c. &c. 



{Concluded from p. 359, vol. i. New Series.) 



The part of the egg which next claims our notice is the air- 

 bag, placed at its obtuse extremity ; this follicle excited in me 

 considerable interest, and was in fact the phenomenon that first 

 directed my attention to the subject of the physiology of the 

 e°;°: ; and when I found that this orsjan had not received the 

 attention which its importance seemed to merit, I was encouraged 

 to pursue its investigation. I am not aware that it exists in the 

 ova of any animals but those of birds : indeed there is a wonder- 

 ful relation between the respiration of oviparous animals before 

 and after their exclusion from the egg ; so, perhaps, birds who 

 enjoy the most perfect species of respiration, are those only 

 whose egg contains a particular organ for the purpose. 



The external shell and the internal membrane with which it 

 is lined, constitute the parietes of the follicnlus a'iris ; its extent 

 in the recent egg is extremely small, and before its exclusion 

 from the uterus, it does not appear to exist ; it would seem to 

 commence at the moment the egg is deposited by the bird ; a 

 small portion of the watery contents of the egg transpire through 

 the shell, and the air then rushes through the obtuse end and 

 inflates the follicle : this is the history of its origin; and its size 

 and subsequent increase are to be explained upon the same 



New Series, vol. ii. b 



