102 



AMPHIBIA. 



communicates with the external air by means of 

 an Eustachian tube passing from it to the 

 fauces. In all the essential parts of this struc- 

 ture, there is but little variation from that 

 which exists in the true reptilia. 



X. The organ of smell. The nares in the 

 perennibranchiate amphibia are, like those of 

 fishes, confined to little more than a slight 

 cavity on the anterior part of the head, and 

 having no continued canal by which they can 

 communicate with the cavity of the mouth. In 

 the proteus the similarity of this organ to that 

 of fishes is so complete, that even the pli- 

 cated radiations of the lining pituitary mem- 

 brane are almost exactly imitated. It is of 

 considerable size, and is contained in a length- 

 ened canal or cavity, the parietes of which are 

 in no part osseous. The nostrils terminate im- 

 mediately under the upper lip. The olfactory 

 nerves are rather large, and no sooner emerge 

 from the cavity of the cranium than they divide 

 into numerous branches of various lengths, 

 which enter every part of the soft pituitary 

 membrane. 



In the more highly developed genera the 

 organ of smell has the more advanced structure 

 which is observed in the reptilia. The nostrils 

 are partly cartilaginous, partly osseous, and 

 extend into the cavity of the mouth, though the 

 posterior openings are placed much more for- 

 ward than in the higher classes of vertebrata. 

 The olfactory nerves enter the nostrils through 

 two openings in the ethmoid bone. The ab- 

 sence of the convoluted and extensive surfaces 

 of the turbinated bones, the entire simplicity of 

 the canal of the nostrils, and the small extent of 

 its surface, must restrict these animals to a very 

 circumscribed enjoyment of this function; and 

 it is probable that the sensibility to odours is 

 much more acute in the aquatic forms, in which 

 the organs of sight and of hearing are so im- 

 perfectly developed, than in the frogs, in which 

 the organs of these senses are much more 

 elaborately formed. 



XI. Of the organ of taste. The sense of 

 taste, in all the amphibia, as well as in fishes, 

 is probably very obtuse. The tongue in the 

 urodela is small, and attached closely at every 

 part. In the anourn, on the contrary, it is 

 developed to an extraordinary degree; it is 

 very long, bifid, and the anterior half is not 

 only free, but, in its quiescent state, doubled 

 back upon the posterior fixed part, and capa- 

 ble of being thrown forwards and again re- 

 tracted with the rapidity of lightning, serving 

 as a most efficient means of arresting the 

 quickest movements of insects, which it con- 

 veys into the back part of the mouth to be 

 swallowed. 



The application of the tongue as an assistant 

 in respiration, by closing the posterior nares, in 

 all higher groups of the class, has been before 

 alluded to. 



XII. The dermal or tegumentary system. 

 The absence of all hard scaly adventitious 

 covering to the skin of the amphibia is one of 

 the most common, or perhaps it may be said, 

 the only universal peculiarity by which they 



are, as a class, distinguished from all reptilia. 

 The amphibious nature of their progressive 

 development, or the existence at the earliest 

 period of even rudimentary branchiae, can 

 scarcely be said to be without exceptions, as 

 several genera have already been mentioned as 

 not having yet been observed in this condition. 

 But the naked skin is a character belonging 

 equally to all, from the serpentiform coecilia to 

 the typically amphibious frog, and the pisciform 

 axoloth and proteus. 



The skin of the aquatic genera is soft, smooth, 

 and furnished with a secreting surface, by 

 means of which it is kept constantly moist, 

 and in a state suitable for that cutaneous respira- 

 tion which strikingly characterises these ani- 

 mals. Many of those which are generally 

 inhabitants of the land, as the terrestrial sala- 

 manders, the toads, and others, are provided 

 with numerous cutaneous glands, which secrete 

 a tenacious milky fluid, which is somewhat 

 acrid, and may perhaps be deleterious if swal- 

 lowed in any quantity ; though the old opinion 

 of the poisonous nature of these animals is 

 altogether without foundation. The fluid which 

 is poured out from these cutaneous follicles in 

 the common salamander is copious, of a milky 

 colour, and consists of mucus, with the addi- 

 tion of some acrid matter, the nature of 

 which is not yet known. From the quan- 

 tity which is suddenly secreted when the ani- 

 mal is injured or any part of the surface 

 irritated, it is not improbable that even the 

 effect of fire may for a few moments be arrested 

 by it ; and thus may have originated the fable 

 of the salamander having the power of remaining 

 unconsumed and unhurt when thrown upon 

 burning coals. The acrid nature of the cuta- 

 neous secretion of the toad was confirmed by 

 the observations of Dr. Davy a few years since. 



The cuticle of these animals is frequently 

 shed ; that of the aquatic species comes off in 

 shreds, and is washed away from the skin. In 

 the toads a very curious process takes place for 

 its removal. When the cuticle has become dry 

 and unyielding, and a new and softer surface 

 is required, the deciduous layer splits down 

 the median line of the back and of the abdo- 

 men at the same time. The whole cuticle is 

 thus divided into two parts. By numerous con- 

 vulsive twitchings and contortions of the body 

 and legs, this separation becomes more and 

 more considerable, and the cuticle is gradually 

 brought off the back and belly in folds towards 

 the sides. It is then loosened from the hinder 

 legs by similar movements of those limbs, and 

 finally removed from them by the animal bring- 

 ing first one and then the other forwards under 

 the arm, and by then withdrawing the hinder 

 leg its cuticle is left under the fore leg. The 

 two portions are now pushed forwards to the 

 mouth, by the help of which the anterior ex- 

 tremities are also divested of it. The whole 

 mass is now pushed by the hands into the 

 mouth, and swallowed at a single gulp. 

 The new cuticle is bright, soft, and covered 

 with a colourless mucus ; the old skin was 

 harsh, dry, dirty, and opaque. This curious 



