62 ANURA 



CHAP. II 



specimens. Nature herself seems to apply hunger as an acceler- 

 ator. Mile, von Chauvin found that the larvae of Urodela 

 normally fast during the transformation, and according to Barfurth 

 the larvae of Rana temporaria eat less after their hind-limbs 

 are fully developed. This is, however, also preparatory for the 

 reorganisation of the gut, which has to be more or less empty 

 during the shortening process. 



The loss of the tail is not due to a sudden dropping off of this 

 organ a crude but by no means uncommon belief but is 

 brought about by a very gradual process of resorbtion. When 

 the fore -limbs begin to break through the skin, the tip of the 

 tail shrinks and becomes black, owing to an increase, or rather 

 concentration, of the pigment cells. The reduction proceeds from 

 the tip forwards until on about the fifth day there remains only 

 a short, conical, black stump. From the beginning of this process 

 of reduction the tail is scarcely used for locomotion, the tadpole 

 rowing with its legs, or it crawls and hops about, although the 

 tail may still be 20 mm. long. The cells of the epidermis atrophy, 

 shrink, and peel off, while those of the cutis, blood-vessels, nerves, 

 muscles, and chorda dorsalis become disintegrated, often under- 

 going fatty degeneration. The leucocytes eat up the debris and 

 other dissolved tissue, and carry it away through the lymphatic 

 vessels, to be used as new building material in the rest of the 

 animal. 



Barfurth asks very properly, Why do these tissues degenerate 

 and die ? Because the vasomotor nerve-fibres cease to regulate 

 the circulation. And why does this trophic influence of the 

 central nervous system stop ? Because the function of the tail 

 becomes superfluous through the appearance of the fore-limbs. 

 The tail is doomed, and degenerates like any other organ without 

 a function. The whole process is, of course, a recapitulation of 

 ancestral, phylogenetic evolution. 



