186 AMPHIBIA. 



developed on the visceral arches ; they usually only reach their full 

 development in larval life. The young are always hatched at an 

 early stage, and undergo a metamorphosis. The larva when hatched 

 recalls the piscine type by the laterally compressed swimming tail, 

 and by the possession of external gills (tig. 627) ; it is still without 

 the two pairs of limbs, which only sprout out as the growth of the 

 body progresses. During these processes the lung sacs which have 

 grown out on the pharynx begin to function, sometimes (Batrctchia) 

 after the external gills have been replaced by internal branchial 

 leaflets covered by the skin, and a branchial slit has been formed on 

 the side of the neck to allow of the exit of the water (fig. 111). 

 Finally the branchial respiration is completely lost in consequence 

 of the atrophy of the gills and their vessels, the tail becomes shorter 

 and shorter and finally, in the Batrachia at least, completely vanishes. 

 In the other groups the later or earlier phases of the developmental 

 series are maintained throughout the whole life ; thus in the 



FIG. 627. Larva of Dactylethra (after Parker). 



Salamandrince the tail, and in the Perennibranchiata the gills also, 

 or at least the external gill slits (Derotrema) persist, and the extre- 

 mities remain rudimentary, or even the anterior pair alone are 

 developed. Accordingly the series of forms indicated by the classifi- 

 cation of these animals offers a strikingly close parallel to the suc- 

 cessive phases of the developmental history of the individual forms. 



The Amphibia frequently live in water only during larval life ; 

 as terrestrial animals in the adult state they choose damp shady 

 places near water, since the cutaneous respiration necessitates in all 

 a moist atmosphere. The food almost always consists of insects and 

 worms, but in larval life principally of vegetable matters. The need 

 of food is, however, relatively small, in correspondence with the low 

 energy of the vital processes, with the sluggishness of their move- 

 ments and psychical manifestations. The Amp/tibia can live for 

 months without food, and, as for example the Batrachia, hibernate 

 buried in the mud. 



