HERPETOLOGY. 



15 



An iiomr this animal is hollowed out into a great number of cells 

 tat Phtsio- i n which the ova, after being extruded by the female, 

 g.^ and fecundated by the male, are placed by the latter ; 

 -_?^L- "id here they remain enveloped in the skin, which con- 

 tracts round them till they are hatched, and ready for 

 enjoying a separate existence. 



Only the Chelonians and Saurian* enter into actual co- 

 pulation, and this act is different in the two orders. It 

 is not certainly known in what manner the male and 

 female turtles and tortoises perform this act. It i* sup- 

 posed, and even asserted by some, that they unite 

 breastplate to breastplate, while others affirm, that the 

 unyon take* place in the manner of quadrupeds. We 

 are not disposed to enter into the minutue of these rep- 

 tilian amours, as we do not think them calculated for 

 a work addressed to general reader*. Those who wish 

 to gratify their curiosity on this part of comparative 

 physiology, may consult the dissertation* of Spallan- 

 zani, and the works of Itocsel, Swammerdam, and 

 Oaudin, already mentioned in our historical notice*. 



The season of copulation connnenrrs early in spring, 

 or a* soon a* the animal* are roused from their whiter 

 state of torpor, and seems to return only once a year : 

 it continue- t.>r a longer or shorter time, in different 

 orders and tribes, generally longest among the frog* 



1 1*. M. 



- >:;- .L. 



enveloped by an 



covering, very 

 In four days, the 



distinct from the exterior mucilage. 

 central germ baa assumed the shape of a kidney bean, 

 and its albuminous covering i* enlarged. In five days, 

 the kidney-shaped embryo has changed it* form to that 

 of a half crescent, though still scarcely increased in 

 '.zc ; but the following day it has become longer, thick- 

 er, and straighter, and the distinction between the 

 outer and inner mucilage is no longer visible. The 

 head, eyes, and mouth are also now obscurely visible, 

 and there is some appearance of a tail. By the seventh 

 day, the size of the tadpole is increased, and the di*. 



and toao*. 



All reptile* are properly oviparous, though in one 

 instance, the salamander, the ova are hatched hi the 

 oviduct. In most of the tribes, the eggs, though nu- 

 merous, are laid distinct from each other ; and, in that 

 oa*c, they are enveloped either bv a calcareous shell, 

 or a membrane resembling parchment. Frogs and 

 tasjQSy however, lay eggs that are connected togctDci** 

 in a kind of bunch, and are of a gelatinous co*iiMnc, 

 ach egg containing in its centre a dark spot, which if 

 the rudiment of the future young, (see Fig. 15.) These 

 oonneeted ears are extruded gradually by the female, 

 and each is fecundated by the male as it escape* from 

 the cloaca. What may be considered as perfect eggs, 

 which are those of the Cheiontan* and Saurian*, are 

 vary similar to those of birds, except that the transpa- 

 rent fluid, which corresponds to the aUmmrn in the 

 Utter, does not coagulate by heat. The eggs of the 

 Chetonian*, and, according to some authors, those of 

 the crocodile, aflbrd good and wholesome nourishment 

 to man. 



have said, that the young of the Batracians un- 

 dergo a mtlamorukotii ; and this is not the least inter- 

 esting part in the physiology of generation in than 

 animals. M. Roesel, in hi* flittoria AUMTM Sotlra- 

 limm, has given a minute account, illustrated by fi- 

 gures, of toe progr*** of the common frog, from the 

 time when the egg is ftrrt fecundated to the completion 

 of the perfect anianai. We shall here present our read- 

 ers with an abstract of this account. 



Two days after the ovum i* excluded, the central 

 spot i* oroewhat enlarged, but still spherical, and is 



tinction of head and tail more evident ; and there are Anatomy 

 also visible the rudiments of the fore feet and of the and - 



fjilU. It has now quitted the egg. At the end of nine 

 day*, the head and body are enlarged, and the tail con- 

 siderably lengthened. Soon after this, the branchiae 

 are so much increased as to be distinctly observed ; but, 

 about the twentieth day, these appendages are with- 

 drawn below the skin, as no longer necessary ; and 

 about four days after, the fore legs, which till now had 

 been almost entirely concealed below the skin, appear 

 externally. The Ixxly of the tadpole is still transpa- 

 rent, and its long intestines are seen extending from 

 head to tail, (see Fig. 16.) In a few days after this, 

 the tail gradually disappears ; the hind legs are cleve- '*' 

 loped ; and, in about two months from the first exclu- 

 sion of the ovum, the animal becomes a perfect frog. 



The metamorphosis of all the Batracians does not pro- 

 ceed exactly in the manner above described. In par- 

 ticular, the tadpole of the liana paradoxa undergoes 

 such remarkable dianges, as to have been mistaken for 

 an animal o'a very different class. These will be no- 

 ticed in a subsequent part of this article. The young 

 of salamanders also differ from the tadpoles of frogs, 

 and have been denominated larvcf. They remain four 

 months in the tadpole state. 



CHAP. IX. 

 On Uybtmation in Reptiles. 



HAVIKO, in the preceding Chapters, described the 

 organization of reptiles, and given a comprehensive 

 view of their organic functions, we have only to con- 

 sider the phenomena that take place in these animals at 

 that season when they begin to lose sense and motion, 

 and sink into a state of torpor. 



I f we except the insect tribes, there are no animals Effect* of 

 to whom heat appears more necessary for enabling them hem * d 

 to exercise their function* with vigour and activity than eold< 

 reptile*. We shall find presently, that by tar the great- 

 er number of the specie* are natives of the torrid zone, 

 ad indeed the few which inhabit these colder regions 

 are comparatively lifeless and inactive. The licit of 

 the sun seem* to increase not only their vivacity and 

 agility, but their sensibility. Cold produces the con- 

 trary effects ; and when this take* place in any consi- 

 derable degree, they become listless and inactive, and 

 would probably perish, if they did not seek for refuge 

 in some situation where they are in some measure shel- 

 tered from the cold in its extreme degree. According- 

 ly, we find that, on the approach of winter, these ani- 

 mals betake themselves to some retreat corresponding 

 to their natural situation. Turtles and freth water tor- 

 toises imbed themselves in the muddy or the sandy bot- 

 toms of lakes and river*, while land tortoises make an 

 excavation in the earth, and there find a temporary 

 grave. Crocodile*, and those other Saurian* which re- 

 ferable them in their usual habitation, find retreats in 

 sand-banks ; while others, especially the Batracians, re- 

 tire to crevices of walls, cavities of stones, clefts of 

 trees, and caverns of mountains \ while a few seek a 

 precarious continuance of warmth by creeping into 

 dunghills. In these retreat*, where they can no longer 

 find their accustomed prey, they gradually sink into a 

 state of insensibility, and appear in a profound sleep, 

 scarcely to-be distinguished from actual death. 



A* this torpidity approaches, their circulation Income? Phenomena 

 languid, their respiration i* extremely *low, their appe- of h y 



