86 



AMniiciA.- 



-REPTILES.- 



-Aivtrinr.iA. 



are very distinct and robust, the cavity of the cranium 

 is verj' small, and even that is by no means filled with 

 brain. The eye in general is contained in a large 

 orbit, in most of them is protected by three lids, and 

 in some is moistened by a fluid analogous to tears. 

 The pupil, except in the tailless species, whose habits 

 are nocturnal, and in which it is angular or linear, is 

 round and very dilatable. There is considerable dif- 

 ference in the structure of the organ of hearing ; in 

 some the auditory canal is visible externally, and in 

 others is not apparent. The nostrils in the great 

 majority of the Amphibia are inclosed in a bony case ; 

 and the internal nostrils open into the middle of tlie 

 palate, as in the frogs, &o.; but in some there is no 

 bony case, and the internal nostrils open between the 

 lips and bones of the palate. The tongue is in general 

 of a good size, is very soft and fleshy throughout, and 

 iu most is armed with a tenacious, viscous secretion. 

 The mouth is very wide and without movable lips. 

 In a few species the teeth are wanting; but in most of 

 them they are present, and are implanted in the jaws. 

 Generally they are numerous, simple, of small but 

 equal size, and close set, either in a single row, or 

 aggregated like the teeth of a rasp. The heart con- 

 sists of a single ventricle and two auricles in the adult. 

 The circulation is simple, part of the blood passing 

 tiu'ough the lungs or gills, and then returning into the 

 general current. The blood is cold, and has large and 

 elliptical globules. They all have lungs, which are 

 formed of large cells, and float in the cavity of the 

 belly. In general they are two, but in some, as in the 

 salamanders, there is only one, which resembles a 

 bladder. In early life they are furnished with gills, 

 analogous to those of fishes, which are supported by 

 cartilaginous arches resulting from the prolongation of 

 the bone of the tongue, the os hjuidcs. When in a 

 perfect state, the greater number lose this gill appa- 

 ratus, whilst others preserve them during life. The 

 act of respiration is carried on by the muscles of the 

 throat, and is somewhat similar to that of deglutition 

 or swallowing, it being necessary for inspiring air that 

 the mouth should be closed. Slost of the Amphibia 

 are oviparous ; some, however, being ovoviviparous. 

 In the males there are no external genital organs 

 visible, and the act of reproduction consists in a simple 

 contact, which endures for several days. The eggs 

 have a membranous envelope, are most frequently 

 laid before fecundation takes place, and increase in size 

 after they are laid. The young undergo a variety of 

 transformations. At first they do not possess limbs, 

 but are furnished with a tail ; and when they become 

 nearly adult, they assume four members, and the 

 greater proportion of them lose their tail. 



The Amphibia almost all live in the water or in 

 moist places. In early life they are herbivorous, but 

 they become carnivorous as they pass into the perfect 

 state. They never, however, feed on the dead car- 

 casses of animals. 



The Amphibia have been arranged in dilTercnt wa)'s 

 by different naturalists. Some take the absence or 

 presence of a tail in the adult state as a means of 

 division into two great groups — the Tailless and the 

 Tailed. Others consider the character of the gills, 



whether caducous or persisting, as a better method of 

 arrangement — the Caducibranchiate and the Peremii- 

 branchiate. " The division adopted by many zoolo- 

 gists of the present day," says Professor Bell, "accord- 

 ing to the mere presence or absence of the tail in the 

 perfect state, is not only liable to the objections which 

 belong to all merely dichotomous arrangements, but 

 appears to be far less natural, and far less consistent 

 with the physiological characters of the groups, than 

 that which is derived from the absence or presence and 

 the duration of the branchix." In the arrangement of 

 the animals of this class adopted by Dr. Gray in his 

 catalogue of the Amphibia in the British Museum, and 

 wliich we propose following in these pages, the struc- 

 ture of the nostrils, with the condition and duration of 

 the gills, are the principal characters relied upon. 



The greater proportion, as we have before observed, 

 have the nostrils inclosed in a bony case, and open 

 internally on the sides of the middle of the palate. 

 These form the group Tritones. The others, which 

 have no bony case to include the nostrils, and have 

 them opening internally between the lips and the bones 

 of the palate, form the group Sikenes. 



The first group, Tuitones, is divided into three 

 Orders : — 



I. BateaciiiA, containing the Frogs, Toads, and 

 Salamanders, and distinguished by the well-developed 

 gill of the young animals disappearing when they reach 

 the mature form, and being then provided with well- 

 dbveloped lungs and four limbs. 



II. PsEUDOSAUUlA, Containing the curious and sin- 

 gular animals called the Ilell-bender (Proionojisi's), 

 and the Congo snake (Amphiuma) ; aiid distinguished 

 bj' their having the gill rudimentary or internal, with 

 the gill apertures i)ermancnt throughout life. The 

 limbs, which are four in number, are either short or 

 almost rudimentary. 



III. PsEUDOPiiiDiA, containing the anomalous- 

 looking animals called the Cfficilia; ; and distinguished 

 by having a rudimentary or internal gill like the pre- 

 ceding order, but with the gill apertures, which are on 

 the side of the neck, becoming closed in the adidts. 



The second group, Siuenes, contains but few spe- 

 cies, and is divided into two Orders : — 



I. Meantia, containing the well-known animals 

 the Proteus and Siren ; and characterized by their 

 having well-developed gills which remain throughout 

 the whole life of the animal, rendering them, as they 

 possess lungs also, truly amphiliious. The limbs in 

 some are four in number, in others only two, but they 

 are only weak and rudimentary organs. 



II. PSEUDOICHTHYAS, containing the very interest- 

 ing but disputed animal called the Mud-fish {Lepido- 

 siren) ; and characterized by having both an external 

 and an internal gill and four very rudimentary and 

 elongate, narrow limbs resembling the fins of fishes. 



The animals contained in this order appear to con- 

 nect the Reptilian Class with that of the Fishes, and 

 by Professor Owen, Sir John Richardson, and some 

 others, are placed amongst these latter animals. As 

 Sir John Richardson is engaged on the drticle Fishes 

 for this work, we will leave the further notice of these 

 curious creatures to him. 



