498 The Embryology of Hylodes Martinicensis 



are Typhlonectes compressicaiida, and Dermophis thomensis, two 

 viviparous species, Hypogeophis, in which the eggs are terrestrial and 

 the larval life is completed within the egg-membranes, and Ichthy- 

 ophis glutinosns, with early stages out of the water ; and among the Anura 

 are a number of forms recently enumerated by several writers." 



The facts as far as they are known in regard to the development of 

 the exceptional forms point to the interpretation that they are descended 

 from forms which originally had aquatic larvae. 



It is to be noted that among Anura, there are no known cases of inter- 

 nal fertilization and viviparity.' 



It seems clear, from what has been described of the habitats, that a 

 form with a free-swimming larva would not survive in some at least of the 

 regions where the animals are found. Salamandra atra lives in high 

 Alps, where the water runs swiftly. Hylodes and Eana opisthodon also 

 live where there are no pools. In the latter cases, the larva and adult 

 no longer inhabit two different environments, but the embryo has become 

 adapted to the environment of the adult of the original form. 



There are other ways in which the difficulties of insufficient water are 

 met. Development may be hurried through (in Lythodytes latrans) in a 

 I'ain pool, where the supply of water is uncertain, or the tadpoles may 

 be provided for in such a way as to survive a drought, as in Cystignathus 

 mystaceus. In such a case as that of Pipa, in which the eggs are carried 

 on the back, while the parent stays in the water, the advantage of the 

 habit is not obvious at present. 



The various adaptations involve in different degrees not only the 

 larvae but often the instincts and certain structures of the parents (as 

 when pouches are developed). 



Whatever the cause or origin of the adaptations may be, it is found 

 that, with a few exceptions, the larvae or embryos of all the forms still 

 retain some of the organs characteristic of the free-swimming larva. 

 These organs are not, however, always used in the same way, or even 

 for the same purpose as in the aquatic larva. In some cases (and among 

 them Hylodes) all the larval organs are not present, and furthermore 

 some new organs which are not found in the larva occur in the embryonic 

 forms. 



The most patent differences in the requirements of the aquatic larva 

 and of the terrestrial or viviparous embryo concern nutrition and respira- 

 tion. In the embryonic form there is the necessity for a special food 



* Brandes and Schoenichen, oi. Wiedersheim, oo. Sampson, oo. 

 ° In Pipa, fertilization takes place perhaps in the oviduct, which is curiously 

 protruded over the back of the female when the eggs are laid. 



