ii FCETAL APPENDAGES. 87 



young animal, are contained in a sac attached to 

 the rudimentary intestine, and termed the yelk 

 sac, or umbilical vesicle. Two membranous bags, 

 intended to subserve respectively the protection 

 and nutrition of the young creature, have been 

 developed from the skin and from the under and 

 hinder surface of the body; the former, the so- 

 called amnion, is a sac rilled with fluid, which 

 invests the whole body of the embryo, and plays 

 the part of a sort of water-bed for it; the other, 

 termed the allantois, grows out, loaded with 

 blood-vessels, from the ventral region, and eventu- 

 ally applying itself to the walls of the cavity, in 

 which the developing organism is contained, en- 

 ables these vessels to become the channel by which 

 the stream of nutriment, required to supply the 

 wants of the offspring, is furnished to it by the 

 parent. 



The structure which is developed by the inter- 

 lacement of the vessels of the offspring with those 

 of the parent, and by means of which the former 

 is enabled to receive nourishment and to get rid 

 of effete matters, is termed the Placenta. 



It would be tedious, and it is unnecessary for 

 my present purpose, to trace the process of de- 

 velopment further; suffice it to say, that, by a long 

 and gradual series of changes, the rudiment here 

 depicted and described, becomes a puppy, is born, 

 and then, by still slower and less perceptible steps, 

 passes into the adult Dog. 



