604 AMPHIBIA, 
! 
SKELETAL CLEFTs. Aortic ARCHES AorTic ARCHES 
ARCHES. : IN THE Empryo. IN THE ADULT. 
2 ; 
Mandibular. ay Late in develop- | Only a trace per- 
ment vessels sists. 
appear which re- 
present a modifi- 
cation of those of 
a branchial arch. 
Eustachian tube. 
Hyoid. The arch is repre- | Disappears en- 
sented in a less tirely. 
modified form. 
First cleft. 
Carotid arch. 
F.rst branchial. First branchial arch. 
Second cleft. 
Second branchial. Second i Systemic arch. 
Third cleft. 
Third branchial. Third a Atrophies. 
Fourth cleft. 
Fourth branchial. Fourth a Pulmo-cutaneous. 
While these changes are in progress, and as the supply of 
food afforded by the tail begins to be exhausted, the tadpole 
recovers its appetite, but is now exclusively carnivorous, 
feeding on any available animal matter, or even on its 
fellows. The change is not, however, so great as it seems, 
for even at a very early stage animal food is eagerly 
devoured. 
With the change of diet, the abdomen shrinks, stomach 
and liver enlarge, the intestine becomes relatively narrower 
and shorter. The- tail shortens moré and more, and as it 
does so the disinclination for a purely aquatic life seems to 
increase. Eventually it is completely absorbed, the hind- 
Iimbs lengthen, and the conversion into a frog is completed. 
In the reduction of the tail the epidermis thickens and is partly cast, 
partly dissolved ; the muscles break up, and their substance undergoes 
intracellular digestion or is dissolved in the body juices; the notochord 
is repeatedly bent on itself and is also disrupted; the same is true of 
nervous system and blood vessels. It is a pathological process which 
has become normal. Some credit the phagocytes with playing a very 
important part in the reduction of the tail; but others restrict their 
function to engulfing solid particles, such as pigment granules, and say 
that most of the material degenerates until it becomes almost liquid, 
when it passes directly into the vascular fluid. 
In many respects the development of the tadpole is very 
interesting, especially because it is a modified recapitulation 
