200 ZOOLOGY. 
their temporary existence only. Now taking the full series of metamor- 
phoses exhibited by animals of this latter division as the standard, and 
establishing, as we may, a number of successive stages of development 
through which the animal passes from the egg to the adult condition, we 
shall find in the former division instances of different species coming up to 
each one of all these stages, and its progress there arrested, and its then 
condition becoming permanent. This will be more fully illustrated in 
subsequent observations. The characters of the Batrachia urodela, as an 
order, consist, among others, in the permanent tail, the rudimentary ribs, 
the limbs four or two, the absence of a sternum, the simple lungs, the teeth 
in both jaws, and the absence of an external ear. They are distributed 
throughout the north temperate regions of both continents, especially 
Northern America, Asia, Europe, Northern Africa, Japan, and ‘the 
Sandwich Islands. Of all these regions North America is most favored in 
this respect, all the Tremadotera, with two exceptions, and the great 
majority of the Atredodera, being found here. Japan comes next in 
regard to variety of form, although not in number of species; in this 
respect, aS in many others, exhibiting a remarkable relation to temperate 
North America. 
To give some idea of the changes which are exhibited by the tailed 
batrachians, in their progress from the embryonic condition to the adult 
state, we will take a particular example in the case of a species of 
Ambystoma, A. punctata, a salamander quite common in the United 
States, and whose descriptive features will be referred to hereafter. Early 
in April, or towards the end of March, large masses of a gelatinous matter 
may be observed in ditches, pools of water, or mountain streamlets, which 
on closer inspection will be found to consist of a number of hollow spheres, 
about a quarter of an inch in diameter, embedded in or combined together 
by a perfectly transparent jelly. Within each sphere is a dark object, a 
spheroidal yolk, which in the course of some days becomes considerably 
elongated, and exhibits signs of animation. Omitting, as unsuited to our 
pages at present, any account of the embryonic development of the animal, 
we resume its history at the time when its struggles have freed it from the 
shell of the sphere in which it was inclosed. -At this time it is about 
half an inch in length, and consists simply of head, body, and tail, the 
latter with a well developed fin, extending from the head and anus to the 
extremity of the body. Respiration is performed by means of three gills 
projecting from each side of the neck, of very simple construction, 
however, and with but few branches. The absence of limbs is compensated 
by the existence of a club-shaped appendage on each side of the head, 
proceeding from the angle of the mouth, and representing the cirri observed 
in some adult salamanders. By means of these appendages, the young 
salamanders are enabled to anchor themselves securely to objects in the 
water. In the course of a few days a tubercle is seen to form on each 
side, just behind the head and under the gills, which elongates, and finally 
forks at the end, first into two, then three, and at last into four branches, 
thus exhibiting the anterior extremities. with the four fingers, which latter, 
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