114 



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- 

 phosis of the Frog ap- 

 plies 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 through in 

 the egg is still a matter 

 of some doubt. Hy- 

 lodes Martinicensis is 

 one of these forms. 



FIG. 82. TADPOLES AND YOUNG OF THE COMMON FEOG. 



(From Mivart. ) 



1. Recently-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 well-developed 

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

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

 tbe tail. 8. Young Frog. 



The larva no doubt 



acquires within the egg a long tail ; but while Bavay 1 states that it is 

 provided with external gills, which however are not covered by an oper- 

 culum, Peters 2 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 toWyman 3 



1 Annal. de Sciences Nat., 5th Series, Vol. xvn., 1873. 



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



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



