250 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 Tremadolera, 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 

 Ambi/sloma, A. functata, 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 

 Images 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 consti'uction, 

 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, 

 {»roceeding 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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