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 F. 
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 twni- 
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 vesting membranes become more apparent, and an 
opake spot at length appears, the rudiment of the foetus f. 
The manner ia 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, the means of growth are 
more obvious. The blood of the placenta is absorbed by 
the umbilical vem 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. 
+ This last term, as used by Aristotie, 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. 
+ Hater found this opake spot in the sheep on the nineteenth day af- 
ter impregnation. Haiguton observed it in the rabbit on the tenth day. 
