140 METAMORPHOSIS. 



jaw, an immensely long tentacle from each upper lip, and possesses no trace 

 of the primordial horny jaws of the ordinary kind. 



b. " In conformity with these characters the head is extremely flat or 

 depressed, instead of being high and thick. 



FIG. 83. LARVA OF DACTYLETHRA. (After Parker.) 



c . " There are no claspers beneath the chin. 



d. " The branchial orifice is not confined to the left side, but exists on 

 the right side also. 



e. " The tail, like the skull, is remarkably chimaeroid ; it terminates in a 

 long thin pointed lash, and the whole caudal region is narrow and elongated 

 as compared with that of our ordinary Batrachian larvae. 



f. " The fore-limbs are not hidden beneath the opercular fold." 

 Although most Anurous embryos are not provided with a sufficient 

 amount of yolk to give rise to a yolk-sack as an external appendage of the 

 embryo, yet in some forms a yolk-sack, nearly as large as that of Teleostei, 

 is developed. One of these forms, Alytes obstetricans, belongs to a well- 

 known European genus allied to Pelobates. The embryos of Pipa dorsigera 

 (Parker) are also provided with a very large yolk-sack, round which they are 

 coiled like a Teleostean embryo. A large yolk-sack is also developed in the 

 embryo of Pseudophryne australis. 



The actual complexity of the organization of different tadpoles, and their 

 relative size, as compared with the adult, vary considerably. The tadpoles 

 of Toads are the smallest, Pseudophryne australis excelling in this respect ; 

 those of Pseudis are the largest known. 



The external gills reach in certain forms, which are hatched in late larval 

 stages, a very great development. It seems however that this development 

 is due to these gills being especially required in the stages before hatching. 

 Thus in Alytes, in which the larva leaves the egg in a stage after the loss of 

 the external gills, these structures reach in the egg a very great development. 

 In Notodelphis ovipara, in which the eggs are carried in a dorsal pouch of 

 the mother, the embryos are provided with long vesicular gills attached to 

 the neck by delicate threads. The fact (if confirmed) that some of the forms 

 which are not hatched till post-larval stages are without external gills, 

 probably indicates that there may be various contrivances for embryonic 

 respiration 1 ; and that the external gills only attain a great development in 



1 In confirmation of this view it may be mentioned that in Pipa Americana the 

 tail appears to function as a respiratory organ in the later stages of development 

 (Peters). 



