216 OVIPARA. 
do not belong to this first part of our work. It is sufficient 
that we have here pointed out the mutual analogy of the Ovi- 
para, 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, which latter, when young, respire, like Fishes, by bran- 
chie. 
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. om » 
