190 AMPHIBIA 



pendicular rocks in quarries, or trunks of trees, in such a position 

 as to allow the larvae to readily drop into the water when 

 strong enough to swim about and procure their food, this being 

 but a simplified variante of the nests which some of their con- 

 geners are known to produce. 



(i) D. Another form of nest is that offered by a small 

 Engystomatid from New Guinea : Phrynixalus biroi. The 

 large, impregnated eggs, measuring seven millimetres in dia- 

 meter, and only twelve to eighteen in number, are enclosed in 

 a sausage-shaped transparent common membrane, secreted by 

 the female, which is abandoned in mountain streams. As in 

 Hylodes, the whole development takes place within the egg, 

 which the little frog leaves in the perfect condition. No gills 

 have been observed and the large tail serves as a breathing 

 organ whilst the young is in the egg. 



(i) E. In several species of the tropical American genus 

 Hylodes, small tree-frogs related to Leptodactylas, of which the 

 West Indian "Cogni," H. martinicensis, is the best known, the 

 eggs are deposited in damp places, under stones or moss or on 

 the leaves of plants, and are of large size. The metamorphosis 

 is hurried through within the egg, and after subsisting on the 

 large yolk-bag, the young frog hops out as an air-breather, with 

 a mere vestige of the tail which was fully developed and so 

 richly supplied with blood that it no doubt functioned as a 

 breathing organ, no gills or gill-slits having been detected. 



(Fig. 13, A.) 



Another small tree-frog of the family Hylidse, Hylella platy- 

 cephala, from Mexico, is said to lay its eggs in the axils of the 

 leaves of Tillandsia, where it undergoes the whole of its meta- 

 morphosis. 



A large frog inhabiting the Solomon Islands, Rana opis- 

 tJwdon, morphologically very similar to our European species of 

 the same genus, also undergoes the whole of its development in 

 the egg and away from water. The eggs, which measure six 

 to ten millimetres in diameter, have been found in the moist 

 crevices of rocks, with the small frog coiled up, in an ad- 

 vanced state of development, without even a vestige of a tail 

 and differing from the perfect frog only in the presence of 

 several folds of skin on the sides of the belly, the function of 

 which is probably that of breathing organs, like the tail of 



