All reptiles are oviparous animals. Certain species, however, retain their ova in a sort of uterine cavity, formed by a dilatation of the oviduct near its termination in the cloaca, until the development of the embryo is so far ralvaneed that the enveloping membrane bursts previously to the expulsion of the ovum, so that the young are actually born alive—a mode of generation to which the terms ow-viripetraus is applied. The eggs are relatively large, and are furnished with a very large yell:, for the nutrition of the young animal. They are inclosed in a parchment-like shell, which contains rely little calcareous matter. They are usually deposited in warm sandy places, well exposed to the sun, or in dunghills, in which the heat induced by the putrefactive process facititates the final stage of embryonic development. Lizards lay from 8 to 12 eggs, serpents from 10 to 50, tortoises from 20 to 26, and crocodiles from 20 to 60. In this respect they differ widely from the amphibia, some of which lay as many as 1200 eggs. The common opin ion that, after the expulsion of the eggs, the reptiles take no further care of their progeny, is erroneous. Crocodiles and lizards have been observed to watch the places which they have chosen as their nest; and the pythons (at all events, when in captivity) coil themselves around their eggs, and keep up a temperature very considerably above that of the surrounding medium. The sexes are always separate; and the male genera tive organs, which are far more highly developed than in amphibians, present peculiari ;les which, in association with the position of the anal aperture, have been adopted by zocAogists as a basis of classification.
. In relation to their habitat, it may be observed that most of the tortoises and certain serpents are essentially aquatic animals (some inhabiting fresh, and some salt water), which rarely seek the land except for the purpose of laying their eggs. Serpents, bow ever, as a general rule, affect moist places in the neighborhood of water, although some are inhabitants of dry sandy deserts. Lizards for the most part frequent the sandy dis tricts of hot and tropical regions, and either burrow in the ground or live in holes in trees, walls, etc. Reptiles generally predominate in the warmer regions of the globe, in which alone the largest kinds are to be found. In the northern countries, comparatively few species are found, and these pass a great portion of the year in a state of hiberna tion (q.v.) or torpidity. Dr. Carpenter puts down 2,000 as about the probable number of existing species of reptiles. Schinz states that in Europe there are 7 tortoises, 33 ser• pents, and 35 lizards. The most complete treatise on the natural history of reptiles is that of I.M.3. Dumeril and Bidron, in 9 volumes; it is entitled Erpetologie Generale, ou Mist, .21at. Complete des Reptiles (Paris, 1834-54).