14 PROCEEDINGS OF THE AMERICAN ACADEMY 



" These facts, joined with the very significant one, that Jacobson 

 found uric acid in the liquid of the allantois at a very early period, 

 seem clearly to indicate that the primary physiological function of 

 the allantois is to serve as a urinary bladder. This office it serves 

 during the whole period of the persistence of the Wolffian bodies, or 

 until the involution of its neck with the intestine changes the ana- 

 tomical relations of its ducts. Its subsequent function, however, is 

 different, and of a more important character. 



" In the mammalian Vertebrata, the embryo forms vascular and 

 nutritive connections with the mother at so early a period that the 

 new being exists but for a little time under independent conditions. 

 As soon as there is direct vascular connection by means of the 

 chorion, the independent life of the embryo ceases, and its nutrition, 

 respiration, and other necessary functions, are performed by the 

 mother. 



" But until this period, the allantois exercises a most important 

 function, namely, that of respiration. Its surface is covered with a 

 close network of bloodvessels, closely resembling the pulmonary 

 structure of the lower vertebrat-es. 



" In the embryos of the ox and goat, so young that no vascular 

 connection had taken place with the mother, I have seen the provis- 

 ional blood-corpuscles (which are at first only simple epithelial cells) 

 become oxygenated, acquiring a red color, from circulating in these 

 vessels. 



"The allantois is then probably a temporary pulmonary organ; 

 the form of respiration being of the lowest order, and quite in char- 

 acter with the condition of the embryo, that is, aquatic. 



" While performing this function it extends to the chorion, blends 

 with its membranes, and its vessels pass over to it (the chorion.) In 

 this way the independent relations of the embryo cease, and the Al- 

 lantois as a distinct organ entirely disappears. 



" In the oviparous Vertebrata, the embryonic conditions are differ- 

 ent. Of these the birds and true reptiles alone have an allantois and 

 amnion. , Here the functional importance of the allantois appears 

 greater than in the division just described. 



" Undoubtedly it serves here, as in Mammalia, as a urinary bladder 

 during its earliest conditions. But its respiratory function soon ap- 

 pears prominent. It increases rapidly, and ultimately envelops the 

 embryo, yolk-sac, and amnion. With these relations it performs the 



