286 REPTILTA. 



These animals have neither scales nor carapace, but the body is invested with a naked [and 

 moist] skin, [over the surface of which the blood receives much of its oxygenation.] With 

 the exception of one genus, they have no nails to the toes. 



The envelope of their eggs is simply membranous, and in most cases these are fecundated 

 as they issue forth, the male attaching himself to the other sex in order to be simultaneous. 



Their eggs or spawn enlarge very much in the water after thej^ have been laid. The young 

 not only differs from the adult by the presence of its gills, but its feet are only developed by 

 deo'rees, and in several genera there are also a deciduous beak and tail, and intestines of a 

 different form. Some of the species are even viviparous. 



The Frogs {Rana, Lin.) — 

 Have four legs and no tail in their adult state. Their head is flat, the muzzle rounded, the mouth 

 deeply cleft, and the greater number have a soft tongue attached only to the lower part of the gullet, 

 but which extends forward to the jaw, and is doubled back above. Their fore -feet have only four 

 toes, but the hinder sometimes show the rudiment of a sixth. 



Their skeleton is entirely deprived of ribs. A cartilaginous plate, even with the head, t.akes the 

 place of tympanum, and renders the ear visible externally. The eye has two fleshy lids, and a third, 

 which is horizontal and transparent, concealed by the lower one. 



The inspiration of air is produced simply by the movements of the muscles of the throat, which, b\ 

 dilating, draw in the air through the nostrils, and, by contracting, whilst the orifices of the nostrils 

 are closed by means of the tongue, force the air into the lungs. Expiration, on the contrary, is 

 effected by the contraction of the muscles of the lower belly : so that, by opening the belly of the 

 living animal, the lungs will distend without any power of contraction, and by holding open the 

 mouth the animal will become asphyxiated, for want of air sent into the lungs. 



The embraces of the male are excessively prolonged : in reference to which the thumb of this sex 

 is furnished with a spongy swelling, which enlarges during the season, and which is designed to aid 

 in grasping. The eggs are fecundated at the moment they are laid, and the young is termed a tadpole. 

 It is at first provided with a long fleshy tad, and a small horny beak, but with no other apparent 

 members besides certain little fringes at the sides of the neck. These disappear after some days, bu-t 

 Swammerdam assures us that they still exist as gills underneath the skin. The latter-are minute 

 crests, which are very numerous, attached to the four cartilaginous arches placed on each side of the 

 neck adhering to the hyoid bone, and enveloped by a membranous tunic, which is covered by the 

 general skin. The water, entering by the mouth, to bathe the intervals of these cartilaginous arches, 

 passes out either by two orifices or by a single one, according to the species, pierced through the 

 external skin, either on the middle or on the left side of the animal. The hind feet are gradually 

 developed to view, by little and little, while the anterior likewise appear beneath the skin, but do not 

 burst it for some time later. The tail is absorbed by degrees. The beak falls, and occasions the 

 genuine mandibles to appear, which had previously been soft, and were concealed underneath the skin. 

 The gills shrink and are obliterated, leaving the lungs to perform their functions unassisted by them. 

 The eye, which in the Tadpole was only visible through a thinner space in the skin, becomes 

 apparent with its three lids. The intestines, previously very long, slender, and spirally contorted, 

 shorten, and acquire the enlargement of stomach and colon : the Tadpole living solely upon aquatic 

 vegetation, whilst the adult animal preys on insects tind other animal substances. ' Finally, the limbs 

 of the Tadpole reproduce the parts of them that had been mutilated, nearly as in the Newts. 



The particular epoch of each of these several charges varies, according to the species. 



In temperate and cold climates, the perfect animal buries itself, during winter, under ground, or in 

 the mud below the surface of water, where it continues to live without food or respiration, [beyond 

 what of the latter is effected by the surface of the skin] ; although, during the warm season, if it be held 

 for a few minutes only with the mouth open, so as to impede the process of respiration, it perishes. 



The Frogs, properly so called, {Rana, Laurenti), — 

 Have a slender body, and the hind limbs very long, and more or less palmated ; their skin is smooth 

 and shppery ; their upper jaw supplied aU round with a range of minutely fine teeth, and they have an 



