lU 



METAMORPHOSIS. 



surface, and the front limbs appear (fig. 82, 6). With these external 

 changes important internal modifications of the mouth, the vascular 

 system, and the visceral arches take place. A gradual atrophy of 



the tail, commencing 

 at the apex, next sets 

 in, and results in the 

 complete absorption 

 of this organ. 



The long alimen- 

 tary canal becomes 

 shortened, and the, in 

 the main, herbivorous 

 Tadpole gradually be- 

 comes converted into 

 the carnivorous Frog 

 (fig. 82, 6, 7, 8). 



The above descrip- 

 tion of the metamor- 

 pliosis of the Frog ap- 

 pHes fairly to the ma- 

 jority of the Anura, 

 but it is necessary to 

 notice a few of the 

 more instructive diver- 

 gences from the general 

 type. 



In the first place, 

 several forms are 

 known, which are 

 hatched in the condi- 

 tion of the adult. The 

 exact amount of meta- 

 morphosis which these 

 forms pass thi'ough in 

 the egg is still a matter 

 of some doubt. Hy- 

 lodes Martinicensis is 

 one of these forms. 

 The larva no doubt 

 acquires within the egg a long tail ; but while Bavay' states that it is 

 provided with external gills, which however ai'e not covered by an oper- 

 culum, Peters^ was unable to see any traces of such structures. 



In Pipa Americana, and apparently in Pipa dorsigera also if a distinct 

 species, the larva leaves the cells on the back of the mother in a condition 

 closely resembling the adult. The embryos of both species develop a long 

 tail in the egg, which is absorbed before hatching, and according to Wyman^ 



Fig. 82. Tadpoles and young of the common Fkog. 

 (From Mivart. ) 

 1. Eecently-hatched Tadpoles twice the natural size. 

 2. Tadpole with external gills. 2a. Same enlarged. 

 3 and 4. Later stages after the enclosure of the gills by 

 the opercular membrane. 5. Stage with weU-developed 

 hind-limbs visible. 6. Stage after the ecdysis, with both 

 pairs of limbs visible. 7. Stage after partial atrophy of 

 the tail. 8. Young Frog. 



^ Annal. de Sciences Nat., 5th Series, Vol. xvii., 1873. 



2 Berlin. Monatsbericht, 1876, p. 703, and Nature, April 5, 1877. 



3 Proceed, of Boston Nat. Hist. Society, Vol. v., 1854. 



