404 PHILOSOPHY OF ZOOLOGY. 



tent *. It is destitute of bloodvessels. Its neck enters 

 the foetus along with the umbilical cord, and joins with the 

 urachus of the bladder. It is the receptacle of the urine 

 of the foetus. In the allantois of the mare and the sow, 

 there is a fleshy-like mass, which some have considered as 

 a sediment from the urine, but whose nature has never been 

 examined. It has been long known by the name of horse- 

 venom, or hippomanes )*. 



In the same situation as the allantois, but unconnected 

 with the urachus, is found, in some of the digitated qua- 

 drupeds, as the dog and cat, a peculiar organ termed tuni- 

 ca erythroides. It is connected with the mesenteric veins 

 of the foetus, and in the early part of pregnancy is filled 

 with a watery fluid. 



The condition, of the germ, when detached from the 

 ovarium, has not been satisfactorily determined. It is de- 

 stitute of character, and too minute and delicate for accu- 

 rate observation. In the uterus, however, it soon expands, 

 its investing membranes become more apparent, and an 

 opake spot at length appears, the rudiment of the foetus {. 

 The manner in which the whole ovum is nourished at this 

 period, is veiled in obscurity. But after the germ has 

 evolved, and the connection with the uterus been establish- 

 ed by the circulating system, die means of growth are 

 more obvious. The blood of the placenta is absorbed by 

 the umbilical vein of the foetus, and while part is convey- 



* The allantois of the cow is frequently preserved in a dried state, and 

 used to protect the surface of sores from the action of the air. 



t This last term, as used by ARISTOTLE, Hist. An. viii. 24. refers to the 

 mucus on the skin of a foal at birth, which the mother removes by licking; 

 or, as in vi. 18. to the humor ex equarum equientium naturalibus distillans. 



$ HALLER found this opake spot in the sheep on the nineteenth day af- 

 ter impregnation. HAIGBTON observed it in the rabbit on the tenth day. 



