404 Vertebrata. 



definitely that these forms are no longer capable of 

 undergoing metamorphosis.* 



In two genera of the Urodela, Menopoma and Amphiuma, the gills atrophy, 

 but the gill-slits persist, and in many respects the animals remain in a larval, or 

 more con-ectly, in an intermediate condition. 



All living Amphibia are freshwater or terrestrial, they are almost 

 always small or of a medium size, and feed upon Insects and other 

 small animals. In earlier times they were to a certain extent 

 represented by larger forms {see below). With regard to the 

 Greographical Distribution, the remarkable fact, that Urodela belong 

 almost exclusively to the temperate regions of the Northern 

 Hemisphere, may be noticed. 



Order 1. XJrodela, 



The tail is well developed ; the fore and hind limbs about equal, 

 and feeble. The larva has three external gills on each side. 



1. Newts (Triton) have a compressed tail, and on the dorsal side of the 

 hody, both dorsal and ventral to the tail, is a fin, which is most marked at the 

 breeding season, and largest in the males. At spawning time they Uve in water, 

 otherwise on land (the male, however, frequently in water) ; the eggs are laid in 

 the spring, singly, or in short strings on aquatic plants. The newly-hatched 

 larva (Fig. 329 A) exhibits posteriorly on the head, a pair of stalk-like processes, 

 hy means of which it attaches itself to plants ; for hmbs, there are only wart-hke 

 processes, the incipient fore hmbs ; they develop gradually, the anterior first ; 

 the organs of attachment soon disappear. Larval hfe usually lasts some 

 months. In England are found the Large Water Newt (T. crisiatus), 

 with a rough skin; the Small Newt (T. tseniatus), the commonest species; 

 the Palmated Smooth Newt (T. helveticus), -with. a. Siiiorm tip to its tail, 

 rare ; the last two are ahout the same size, the first considerably larger. 



2. The Salamander (SaZamarwZra macMZosa) is an animal of considerable 

 size (up to 18 c/m) ; velvet black, with large irregiilar yellow spots ; no trace of a 

 fin ; tail rounded. In Central and South Europe ; viviparous ; the young ones 

 quite differently colomred ; they are born vrith gills, and hoth pairs of hmbs, and 

 then only are aquatic. It is of interest that the embryo has much longer giU 

 laminse whilst still within the oviduct, than it has later. The Black Alpine 

 Salamander (S. atra), alUed to the one just described, and quite black, occurs 

 in the Alps ; viviparous, beai-ing only two young ones at a time, one in each 

 oviduct {8. maculosa produces a greater nmnher at a birth). There are several 

 eggs in the oviduct, hesides the one which develops, but they merely coalesce, 

 and furnish nutrition for the embryo. The embryo has extraordinarily large 

 gUls, which surroimd a great part of the hody before birth, but atrophy later : 

 metamorphosis thus occurs within the body of the parent ; the Alpine Salamander 

 is bom on dry land, and is never aquatic. 



3. The Axolotl {Siredo-n mexioanus) is distinguished as already mentioned 

 by the fact that, in captivity at least, it does not usuaUy imdergo a metamorphosis, 

 but becomes sexually matm-e in the larval state. The form which does undergo a 



* For instance, in Proteus, that portion of the fourth arterial arch which lies 

 between the ventral aorta and the point of origin of the pulmonary artery is absent,, 

 but it is indispensable for the adult Amphibian. 



