86 Amphibia. REPTILES. Amphibia. 
are very distinct and robust, the cavity of the cranium 
is very small, and even that is by no means fil’ed 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 the 
palate, as in the frogs, &c.; 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 
in 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 
through 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, 
a:ialogous to those of fishes, which are supported by 
cartilaginous arches resulting from the prolongation of 
the bone of the tongue, the os hyoides. When in a 
perfect state, the greater number lose this gill appa- 
ratus, whilst others preserve them during life. 'I'he 
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. Most 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 different ways 
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 Perenni- 
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 branchiae.” In the arrangement of 
the animals of this class adopted by Dr. Gray in his 
catalogue of the Amphibia in the British Museum, and 
which 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 Sirenes. 
The first group. Tritones, is divided into three 
Orders : — 
I. Batrachia, 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- 
developed lungs and four limbs. 
II. PsEUDOSAURiA, containing the curious and sin- 
gular animals called the Hell-bender {Protonopsis), 
and the Congo snake {Amplduma ) ; and distinguished 
by their having the gill rudimentary or internal, with 
the gill apertures permanent throughout life. The 
limbs, which are four in number, are either short or 
almost rudimentary. 
III. PSEUDOPHIDIA, containing the anomalous- 
looking animals called the Cmcilise ; 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 adults. 
The second group, Sirenes, 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 w'hole life of the animal, rendering them, as they 
possess lungs also, truly amphibious. 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 article Fishes 
for this work, we will leave the further notice of these 
curious creatures to him. 
