OCR Text |
Show 216 OVIFARA• do not belong to this :first part of our work. lt is suflicient that we have here pointed out the mutual analogy of the Ovipara, which, as regards the plan on which ~hey 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 t~e purposes of respiration ; it is con· nected with the bladder, and is analogous to the allantoid ofthe Mammalia. It is neither found in FisHes nor in the Batrach· ians, which latter, when young, respire, . }ike Fishes, by bran· chire. _. f Many of the cold-blooded Ovipara do ~Qt bring forth their young until they are developed and ext~icated from their shell, or other membranes, which separated them from the mother. These are called false Ovipara. |