106 



AMPHIBIA. 



genera, as the tritons, is effected by a totally 

 different mode. During the spring, the males 

 acquire a considerable dorsal membrane, which 

 runs the whole length of the back and tail, 

 and is sometimes curiously indented or fringed 

 at its edge. This membrane is gradually lost 

 after the breeding season, and its use appears 

 to be to assist in the act of impregnation. 

 The male, instead of adhering to the female 

 like the frog, swims by her side pursuing her 

 in all her rapid and changing courses through 

 the water, till at length both remaining for a 

 moment quite still, he suddenly turns up, by 

 the assistance doubtless of the dorsal mem- 

 brane, and places for an instant the edges of 

 the cloacal aperture in contact with hers. It 

 is at this instant that the semen is ejected and 

 received. The eggs are afterwards deposited 

 slowly, and comparatively few in number, 

 upon some part of an aquatic plant, on which 

 the female supports herself by holding by her 

 hinder legs. 



When the embryo has gradually acquired 

 its larva development, and is ready for its 

 aquatic life, it bursts the thin membrane which 

 encloses it, and emerges in the fish-like form 

 which has been so often alluded to in this paper. 



XVI. Metamorphosis, The changes which 

 take place in the different organs during the 

 progress of this extraordinary phenomenon, 

 have been already detailed. It remains to 

 trace the general form of the animal from the 

 egg through its larva condition till it receives 

 its permanent form, and to point out some 

 remarkable peculiarities observed in different 

 genera. 



In the frog, the toad, and probably all the 

 anoura, the respiratory organs undergo a double 

 change, the branchiae being first external for a 

 very brief period, and afterwards internal during 

 the remainder of its larva existence. In all 

 the other forms in which branchiae have been 

 detected, they remain external till they are lost. 



The tadpole, whether of the anoura or of 

 the urodela, possesses, at first, as we have seen, 

 the same means of progression as belong to the 

 class of fishes. That of the triton retains its 

 branchiae, co-existent with four perfect legs, 

 until it is about a third of its ultimate length. 

 In the frog the legs which first make their 

 appearance are the hinder ones ; and from the 

 great development of the tail, and the con- 

 tinuous form of the head or abdomen, they ap- 

 pear as if they came through immediately be- 

 hind the head. 



As the terrestrial salamander, though pre- 

 ferring moist places, does not frequent the 

 water, the young have not the opportunity of 

 being developed in that medium ; but as the 

 essential character of their organisation requires 

 that the first portion of their existence should 

 be passed in the condition of a tadpole or larva, 

 we find that the whole of its metamorphosis 

 takes place whilst in the oviduct, where it is 

 found with small branchiae on each side of the 

 neck, which are lost as the animal enters upon 

 its terrestrial existence. Like the viper, there- 

 fore, this animal is ovo-viviparous. 



The arrest of the metamorphosis in the lower 

 or perennibranchiate forms is confined to the 

 organs of locomotion in part, to those of cir- 

 culation, and of respiration. The organs of 

 reproduction receive their full development, 

 though even in these there is a considerable 

 resemblance to those of the fishes. 



One of the most remarkable peculiarities in 

 the whole of this class, with regard to the sub- 

 ject now under consideration, is the reproduc- 

 tion and metamorphosis of the pipa or Surinam 

 toad. It has long been known that the eggs 

 are developed in cells on the buck of the 

 mother; but the facts connected with this 

 curious circumstance have only of late years 

 been ascertained. It is now established that 

 the cells on the skin of the female are not 

 persistent, but grow as the eggs enlarge, and 

 are removed after the young leave them. The 

 male impregnates the eggs as the toad, but 

 immediately places them on the skin of the 

 mother's back; here they are attached by a 

 tenacious mucus, and the skin gradually thickens 

 in the interstices, forming at length a cell around 

 each. In these cells the young ones not only 

 leave the eggs, but actually undergo their 

 metamorphosis ; and when they leave the back 

 of the parent, they have lost all the characters of 

 the tadpole, and have become perfect animals. 



It is impossible to contemplate the structure 

 and habits of this remarkable class of animals 

 without being struck by the many interesting 

 points which they offer for the investigation of 

 the physiologist. Whether we consider the 

 evident and perfect transition which many of 

 them present, from the form and structure of 

 an inferior to that of a superior type or organiza- 

 tion, the facilities which they afford us of 

 tracing, as it were under the eye, those mys- 

 terious changes and grades of development 

 which in most cases are accessible only at par- 

 ticular epochs, or are wholly concealed during 

 their progress in the hidden recesses of the 

 reproductive organs, or whether we view the 

 modifications which they present of the respi- 

 ratory and other important functions of life, it is 

 not, perhaps, saying too much to aver that there 

 is scarcely any class of animals which invites the 

 study and contemplation of the lover of physi- 

 ological science by phenomena at once so varied 

 and so interesting as the Amphibia. 



BIBLIOGRAPHY. Boddaert, Abhand. von Am- 

 phibien, in Bcrl. Gesels. Naturf. Freunde B. ii. S. 

 369. Gray, on the class of animals called by Lin- 

 naeus Amphibia. Phil. Trans. 1789, p. 21. Schnei- 

 der, Amphib. Physiol. spec. 4to. Frft. a M . 1790-92. 

 Ditto, Hist. Amphib. nat. et literar. 8vo. Jena, 

 1799-1801. Laurenti, Synops. Reptil. 8vo. Vim. 

 1768. Meyer, Synops. Reptil. 8vo. Getting. 1795. 

 Latreille, Contin. of Buffon. Hist. Nat. des Am- 

 phib. Ditto, Hist. Nat. des Salamandres, 8vo. 

 Paris, 1800. Brongniart. Essai d'une Classif. 

 Nat. des Reptiles. 'Societe Philom. A. iii. T. 2. 

 Oppel, Ord. Fam. u. Gattung. der Amphibien. 4to. 

 Munich. 1811. Merrem, Tent. System. Amphib. 

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 nat. Ranar. nostrat. fol. Norib. 1746-61. Ed. Alt. 

 auct. germ. s. t. Naturgesch. der Froesche, &c. 

 fol. Niirnb. 1800-15. Steinheim, Entwickelung d. 

 Frosche.8vo.Hamb. 1820. Hasselt, Demctamorph. 



