Glass 3. Amphibia, 



403 



much more piscine (p. 394) early, than in final stages. When the 

 tadpoles hatch, they are generally somewhat unlike the fully-developed 

 larval form; for example, the limbs are not present, or are merely 

 indicated, and, on the 

 head, there are frequently 

 ■organs of attachment, 

 which atrophy after a time 

 (Pig. 327 ^— £,and3294). 

 The metamorphosis 

 itself, that is, the change 

 from the larval to the 

 perfect form, is completed 

 somewhat suddenly ; the 

 changes are accomplished 

 in quite a short time. 

 The size attained before 

 metamorphosis varies ; 



closely allied species often 

 differ considerably in this 

 respect ; for example, with- 

 in the genus Eana, the 

 larva of the Edible Prog 

 is very large, that of the 

 Orass Prog, on the other 



hand, rather small; growth is not usually completed at metamorphosis 

 (as in Insects) but continues for some time.* In some Urodela, viz. 

 in certain Tritons, it has been noticed that the larvae somet/me's 

 grow beyond their customary size, and become sexually mature 

 :as larvssj whether they afterwards undergo metamorphosis is 

 unknown. The same thing occurs normally in the larva of a 

 Mexican Salamander the Axolotl {Siredon mexicanus) , a.t least in 

 those individuals which have been kept in confinement ; they are, as 

 a rule, sexually mature during the larval period, and do 'not 

 undergo a metamorphosis ■ this happens only exceptionally, and then 

 before sexual maturity. Lastly, there are a few Urodela, the 

 Perennibranchiata (genus Proteus, etc.), which remain in 

 the larval condition and never assume the adult form. These forms 

 are like larvae in all respects excepting the development of the 

 reproductive organs; in some points, however, they have undergone 

 degeneration ; m Proteus, for instance, the lungs, compared with the 

 size of the animal, are very poorly developed, and they are of iust 

 as little respiratory significance as in the larva. The retrogressions 

 are m part of such a character as to render it possible to state 



1^^.329. LaTTas of the large Triton. 4 newly 

 hatched, from the side and below. B la days old. 

 about 5 weeks old. (A x about 5, B 3 — 4, 

 scarcely x 2). a anus, / fore limb, g giUs, s organ 

 of attachment. — After Eusconi. 



' The larva; of a South American Frog- {Pseitdis paradom) are huge. 



D D 



