104 



AMPHIBIA. 



r, described by Dr. Milne Edwards, 

 formed by duplicatui-es of the lining mem- 

 brane of the branchial cavity. The eel too, as 

 i> well known, will live for a long time out of 

 water, from its branchial cavity being capable of 

 retaining a sufficient quantity of water to bathe 

 the branch iiv for a considerable time, thus 

 preserving those organs in a respirable state. 



XI II. Of' transpiration ami i>f secretion. 

 The particular condition of the skin already 

 d escribed, naked and consisting of a moist 

 mucous surface, would render it probable that 

 cutaneous transpiration should be exceedingly 

 extensive and rapid in these animals : this is 

 in fact the case to such an extent, that when 

 exposed to too great a degree of heat, the eva- 

 poration of transpired fluid is sufficient to pro- 

 duce a very rapid decrease in the weight of the 

 animal ; which, if exposed for a sufficiently 

 long period to its influence, becomes almost 

 dried up and d 



One object, and that not an unimportant 

 one, of the sensible transpiration of fluid in 

 these animals, the frogs especially, is un- 

 doubtedly to preserve the skin in a condition 

 fit for the" performance of that cutaneous respi- 

 ration which has been described. But its still 

 more obvious purpose is to aflbrd a quantity of 

 fluid for evaporation from the surface, in order to 

 reduce and equalize the temperature of the body 

 when exposed to a degree of heat, sufficient to 

 incommode or injure it. This will appear 

 very reasonable when we reflect that these ani- 

 mals will die in a few minutes, if placed in 

 water of 107 decrees of Fahr., though respiring 

 freely with the head above the water, whilst, 

 on the contrary, they will support for hours the 

 action of damp air of the same temperature. 



The water which is thus transpired is not 

 the result of the absorption of fluids taken in 

 by the mouth, for these animals do not appear 

 to drink. It is received by absorption on the 

 surface of the skin, to which part it is after- 

 wards restored when necessary. But in order 

 to be re idy whenever circumstances call for its 

 use. the fluid thus absorbed is conveyed into a 

 membranous cavity, formed generally of two 

 lobes, opening into the cloaca, where it is re- 

 tained, to be again absorbed, and again con- 

 , d to the surface for the purposes just men- 

 tioned. \Yhen a frog is suddenly alarmed, or 

 seized, it ejects from its cloaca a quantity of 

 pure, limpid water, for the purpose of lighten- 

 ing itself, that it may leap with greater facility. 

 This fluid is expelled from the sac in question, 

 and is often mistaken for urine, and the sac for 

 a urinary bladder. Hence, if a frog be kept in 

 a moist situation, without having access to 

 water in any form but in vapour, the skin is 

 always kept moist, and the water-bag a 

 filled. 



Such is the function attributed in the first 

 place by Townson to the sac in question, and 

 after him by Dumeril, Altena, and others : but 

 Cuvier. Dr. Grant, and many other anato- 

 mists consider that it is the true urinary blad- 

 der. That Townson's opinion is correct ap- 

 pears, says Altena, from the circumstance that 



the ureters do not terminate in the bladder, but 

 in the rectum itself." Dr. Grant states, that on 

 the contrary, "the bladder receives the ureters." 



The kidneys are of a lengthened form, in the 

 aquatic genera, but are shorter in the frogs and 

 other anoura. 



XIV. On the restoration of lost parts. 

 The fact that parts lost by accident, or re- 

 moved for the purpose of experiment, become 

 reproduced in many of the lower animals, has 

 been known for aces. The actual multipli- 

 cation of the species in many, perhaps all the 

 polygustrie animalcula, by spontaneous sepa- 

 ration, that of the hydra" by artificial division, 

 the restoration of lost anus in the different 

 species of asterias, of the anterior or posterior 

 extremity of the body in the earthworm, of 

 the claws of the lobster, and other Crustacea, 

 and of portions of the head in the pulmo- 

 niferous mollusca, are, all of them, phenomena 

 which have attracted the attention, and occu- 

 pied the experiments of physiologists, at va- 

 rious periods. The experiments of Plateretti, 

 Spallanzani, Murray, Bonnet, and others, have 

 shewn that it is not in the invertebrate forms 

 alone that we are to look for this phenomenon, 

 but that the amphibia, and even some reptilia, 

 will reproduce either the limbs or the tail, 

 when removed. This restoration of the tail 

 in the saurian reptiles is indeed a common 

 occurrence, and it often happens that the new 

 tail is double through the whole of the restored 

 length. 



Of all the observers of this curious phe- 

 nomenon in the amphibia, Bonnet* stands pre- 

 eminent for the laborious and patient zeal with 

 which all his experiments were conducted, no 

 less than tor the conscientious strictness with 

 which they are recorded. In many experi- 

 ments he cut off the anterior or posterior limbs 

 of the common water salamander or triton, 

 which he found to be invariably restored, and 

 even the toes were reproduced, and acquired 

 some degree of motion. The tails were also 

 amputated at various distances from the base, 

 and were always renewed. The same limb 

 was in some cases removed and restored four 

 times consecutively. In all cases it was ob- 

 served that warmth encouraged and that cold 

 retarded the regeneration of the part. The 

 restored portions were not generally well- 

 formed, but in some instances varied by t\ 

 in others by defect. One of the most t 

 ordinary results was that which followed the 

 extirpation of an eye from one of these ani- 

 mals. In the course of a year this organ was 

 completely restored, and its organization was 

 found to be perfect. 



Dumeril records a remarkable experiment 

 of this nature, in his latest work on the rep- 

 tilia. The subject was the triton mmr- 

 monttus. Three-fourths of the head were cut 

 off, and the animal was deposited at the bot- 

 tom of a large vessel having half an inch depth 

 of water, which was constantly renewed. It 

 continued to live, and to move slowly. The 



* (Euvres. iu 4to. Neufchatel, 1769. 



