Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/103/
AMPHIBIA. 91 
of groups having more striking distinctive cha¬ 
racters, there is not, perhaps, a more interesting 
and satisfactory instance in the whole range of 
the animal creation than is afforded us in the 
class of amphibia : a circumstance which can 
only be fully appreciated by following out the 
structure of each system of organs, first as it 
exists temporarily in the tadpole, and ultimately 
in its permanent condition in the perfect animal. 
The class has been variously divided into 
groups according to the different views of the 
naturalists by whom they have been arranged. 
The division adopted by many zoologists of 
the present day, according to the mere preseuce 
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 less consistent 
with the physiological characters of the groups 
than that which may be derived from the 
absence or presence and the duration of the 
branchiæ. Thus the frogs and toads, which 
in the adult state have not the vestige of a tail, 
and the salamanders and tritons, which retain 
that organ through life, all agree in the early 
possession of branchiæ, which are subsequently 
lost and replaced by true lungs, and in un¬ 
dergoing consequently a total change in the 
medium of their respiration; whilst the pro- 
teus and the siren retain their branchiæ, with 
lungs, (rudimentary at least,) and probably 
throughout life possess synchronously the two¬ 
fold function of aquatic and atmospheric re¬ 
spiration. The amphiuma and menopoma have 
not as yet been observed to possess branchiæ 
at any period of their existence, though further 
observations are necessary to warrant the con¬ 
clusion of an absolute non-existence of a meta¬ 
morphosis in these genera. 
It appears to me that no one arrangement 
hitherto given sufficiently distinguishes the 
different forms ; and I venture to propose the 
following modifications as more consistent with 
the diversities of structure in the different 
groups. 
Class Amphibia. 
Order 1.—Amphipneurta. 
Body elongate, formed for swimming. Feet 
either four, or two anterior only. Tail com¬ 
pressed, persistent. Respiration aquatic by 
means of branchiæ, throughout life, co-existing 
with rudimentary lungs. Branchiæ external, 
persistent. Eyes with palpebræ. 
Genera, Proteus, Siredon, Menobranchus, 
Siren, Pseudobranchus. 
Order 2.—Anoura. 
Body short and broad. Feet during the tad¬ 
pole state wanting ; afterwards four, the hinder 
ones long and formed for leaping. Tail before 
the metamorphosis, long, compressed ; after¬ 
wards totally wanting. Ribs wanting. Ver¬ 
tebra few and anchylosed. Tympanum open. 
Respiration at first aquatic by branchiæ ; after¬ 
wards atmospheric by lungs. Branchiæ at first 
external, but withdrawn within the chest before 
the metamorphosis. Impregnation effected ex¬ 
ternally during the passage of the ova. 
Genera, Pana, Hyla, Ceratophrys, Bufo, 
Rhinella, Otilopha, Ductylethra, Bombinator, 
Breviceps. 
Order 3.—Urodela. 
Body long, slender. Feet always four. Tail 
long, persistent. Ribs very short. Respi¬ 
ration at first aquatic by external branchiæ, 
afterwards atmospheric by cellular lungs. Ver¬ 
tebra numerous and moveable. Tympanum 
concealed. Impregnation internal. 
Genera, Salamandrina, Salamandra, Molge. 
Order 4.—Abranchia. 
Body long, formed for swimming. Feet four. 
Cranium solid. Tail compressed. Respi¬ 
ration by means of lungs only : branchiæ none. 
No metamorphosis known. 
Genera, Menopoma, Amphiuma. 
Order 5.—Apod a. 
Body elongate, slender, anguiform. Feet 
none. Tail veiy short, almost wanting. Lungs 
one larger than the other. (The existence of 
branchiæ at any period of life unknown.) Ribs 
very short. Sternum wanting. Ears concealed. 
Impregnation unknown, probably internal. 
Genus, Cacilia. 
I. Osteology.—The changes which take place 
in the habits and formation of these animals, 
in their passage from the tadpole or pisciform 
state to their adult and permanent condition, 
are not confined to any one system of organs 
or of functions. The skeleton, the organs of 
motion, of sensation, and of digestion are not less 
the subject of these changes than those of 
respiration and circulation : it will, therefore, 
be necessary, in treating of each system of 
organs, to describe not merely their structure 
in the perfect state, but the less advanced 
grade of organization from which they emerge 
in passing from the condition of a fish to that 
of a reptile. 
In the adult state, however, they are found 
to vary considerably in the form and composi¬ 
tion of the skeleton, according to their habits, 
and to the existence or absence of a tail. The 
principle of compensation, or, in other words, 
the extreme developement of one set of organs 
at the expense of another, which is so often 
seen to take place in every form of animals, 
is here strikingly illustrated. In the frogs, 
whose movements on land, from their feeding 
chiefly on terrestrial prey, are necessarily ex¬ 
tensive, we find the hinder legs developed to 
an extraordinary degree, for the purpose of 
enabling them to take enormous leaps, by 
which they not only seek or pursue their prey 
at a distance from the water, but rapidly 
escape from danger, and rapidly regain their 
place of refuge in the nearest pond or rivulet. 
As it is evident that a long tail and a generally 
elongated body, with a flexible spine, would 
be not only useless but inconsistent with these 
habits, we find these aijimals absolutely tail-
        

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