AMPHIBIA. 139 



The eyes, hitherto concealed under the skin, become exposed 

 on the 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 alimentary canal becomes shortened, and the, in 

 the main, herbivorous Tadpole gradually becomes converted 

 into the carnivorous Frog (fig. 82, 6, 7, 8). 



The above description of the metamorphosis of the Frog applies fairly to 

 the majority of the Anura, but it is necessary to notice a few of the more 

 instructive divergences from the general type. 



In the first place, several forms are known, which are hatched in the 

 condition of the adult. The exact amount of metamorphosis which these 

 forms pass through in the egg is still a matter of some doubt. Hylodes 

 Martinicensis is one of these forms. 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 operculum, 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 to Wyman 3 

 P. Americana is also temporarily provided with gills, which atrophy early. 



The larva of Rhinoderma Darwinii is stated by Jiminez de la Espada to 

 be without external gills, and it appears to be hatched while still in the 

 laryngeal pouch of the male. In Nototrema marsupiatum the larvae are also 

 stated to be without external gills. 



Amongst the forms with remarkable developments Pseudis paradoxa 

 deserves especial mention, in that the tadpole of this form attains an 

 immensely greater bulk than the adult ; a peculiarity which may be simply a 

 question of nutrition, or may perhaps be explained by supposing that the 

 larva resembles a real ancestral form, which was much larger than the 

 existing Frog. 



Another form of perhaps still greater morphological interest is the larva 

 of Dactylethra. The chief peculiarities of this larva (fig. 83) have been 

 summarized by Parker (No. 107, p. 626), from whom I quote the following 

 passage : 



a. " The mouth is not inferior in position, suctorial and small, but is 

 very wide like that of the ' Siluroids and Lophius ;' has an underhung lower 



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



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



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



