ft 



216 OVIPARA. 



do not belong to this first part of our work. It is sufl&cient 

 that we have here pointed out the mutual analogy of the Ovi- 

 paraj which, as regards the plan on which they are constructed, 

 is greater than that of any one of them with the Mammalia. 



Oviparous generation consists, essentially, in this the 

 young animal is not attached by a placenta to the parietes of 

 the uterus, or of the oviduct, but remains separated from it 

 by its most external envelope. Its aliment is prepared before 

 hand, and enclosed in a sac attached to its intestinal canal; 

 this is what is called the vitellus, or yolk of egg, of which the 

 young animal is a sort of appendage, at first imperceptible, 

 which is nourished and augmented by absorbing the fluid of 

 that yolk. Such of the Ovipara as breathe with lungs have 

 the egg furnished with a highly vascular membrane, which 

 appears to serve for the purposes of respiration ; it is con- 

 nected with the bladder, and is analogous to the allantoid of the 

 Mammalia. It is neither found in Fishes nor in the Batrach- 

 ians, w^hich latter, when young, respire, like Fishes, by bran- 

 chiae. 



Many of the cold-blooded Ovipara do not bring forth their 

 young until they are developed and extricated from their 

 shell, or other membranes, which separated them from the 

 mother. These are called false Ovipara. 



