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Show 2 REPTILIA. In cold or temperate climates almost aU of them pass the winter in a state of torpor. Their brain, which is proportionally very small, is not so essentia1ly requisite to the exercise of their animal and vital faculties, as to the members of the two first classes; their sensations seem to be less referred to a common centre, for they continue to live and to exhibit voluntary motions, long after losing their brain, and even after the loss o~ their head. A communication with the nervous system IS also much less necessary to the contraction of their fibres, and their muscles preserve their irritability after being sev~red from the b?dy much longer than those of the precedmg classes; their heart continues to pulsate for hours after it has been torn away, nor does its loss prevent the body from moving for a long time. The cerebellum of several has been observed to be extremely small, a fact which tallies with their slight propensity to motion. The smallness of the pulmonary vessels permits reptiles to suspend the process of respiration without arresting the course of the blood; thus they dive with more facility, and remain longer under water than either the Mammalia or Birds. The cells of their lungs, being less numerous, because they have fewer vessels to lodge on their parietes, are much wider, and the organs themselves sometimes resemble simple sacs with scarcely any appearance of cells. Although some of them are incapable of producing audible sounds: they are all provided with a trachea and larynx. Their blood not being warm, there was no necessity for te.guments capable of retaining heat, so that they are covered With scales or simply with a naked skin. The females have a double ovary and two oviducts; the males of several genera have a forked or double penis those of the last ?rder, the Batrachians, have none. ' No re. ptile hatches I't 's eggs, an d m· several genera of the Batrachu. e' the. y are ~•' e cun d a t e d af ter t h e.i r exclusi.O n from the female, ,m whiCh case the egg is enveloped by a membrane only. fhe young of this latter order, on quitting the egg have the form and bra nc· h·u e of FI' s h es, and some of I. ts genera' REPTILIA. 3 preserve these organs, even after the development of t~eir lungs. In several oviparous reptiles, the Colubers particularly, the young animal in the egg is formed and considerably advanced at the moment of its exit from the mother; and there are even some species which may be rendered viviparous by simply retarding that epoch.(l) The quantity of respiration in Reptiles is not fixed like that of the Mammalia and Birds, but varies with the proportion of the diameter of the pulmonary artery compared to that of the aorta. Thus Tortoises and Lizards respire more than Frogs, &c.; and hence a much greater difference of sensibility and energy than can exist between one of the Mammalia and another, or between Birds. Reptiles accordingly present an infinitely greater variety of forms, motions, and properties than are to be found in the two preceding classes, and it is in their production that Nature seems to have amused herself by imagining the most fantastic sl1apes, and by modifying in every possible way the general plan she has followed in the construction of the Vertebrated animals, and in the Oviparous classes especially. The comparison, however, of their quantity of respiration and of their organs of motion, has enabled M. Brogniart to divide them into four orders,(2) viz. The CHELONIA, or ToRTOisEs, whose heart has two auricles, and whose body, supported by four feet, is enveloped by two plates or bucklers formed by the ribs and sternum. The SAURIA, or LizARDs, whose heart has two auricles, and whose body, supported by four or two feet, is covered with scales. The OPHIDIA, or SERPENTs, whose heart has two auricles, and whose body always remains deprived of feet. The BA TRACHIA, whose heart has but one auricle, and whose body is naked, most of which pass, with age, from the (1) The Colubers, for instance, when deprived of water, as proved by the experiments of M. Geoffroy. (2) Al. Brogniart, Essai d'une Classification Naturelle des Reptiles, Paris, 1805, and in the Mlm. des Savants Etrang., tom. 1, p. 587. |
