METAMORPHOSIS 6 1 



Meanwhile the hmgs are being developed, and the tadpole 

 occasionally rises to the surface to breathe air. The gills, which, 

 as has been explained elsewhere, are less ancestral than they are 

 larval organs, degenerate, and all the organs are modified for the 

 coming terrestrial life. The fins of the tail are absorbed, the 

 horny armature of the mouth and lips is shed in pieces and makes 

 room for the true teeth, the eyes recei^'e lids, and the whole 

 cranium, especially the apparatus of the jaws, undergoes the final 

 modifications — widening and lengthening of the mouth, arresting 

 of the mento-Meckelian cartilages, elongation of the Meckelian 

 cartilages or lower jaw proper, shifting backwards of the sus- 

 pensorium, and lengthening of its orbital process to form the 

 pterygo-palatine bridge. 



The tadpole ceases to feed, the whole intestinal canal is voided 

 of its contents, and by " histolysis " is thoroughly rebuilt, becoming 

 wider and shrinking to about one-sixth of its original length, 

 — undoing thereby the spiral — preparatory for the coarser food, 

 which consists of insects, worms, and other strictly animal, living- 

 matter. Hitherto the tadpoles have lived on " mud," confervae, 

 Diatoms, rotting vegetable and animal matter. The anal tube 

 collapses, becomes ultimately absorbed, and a new vent is formed 

 at and below the root of the tail. 



Barfurth ^ has made interesting observations and experiments 

 with regard to the absorption of the tail and other organs which 

 disappear during the metamorphosis. This is retarded by 

 low temperature ; it is accelerated by rest and freedom from 

 mechanical disturbances, as, for instance, concussion of the water. 

 Hunger shortens or hurries on the last stages of metamorphosis, 

 the absorption of the tail taking place in four instead of five days. 

 Amputation of the {ail has no retarding influence ; it is followed 

 at once by regeneration, although the tadpole may be on the 

 verge of reducing the tail. Whilst hungering the whole organism 

 draws upon its available store of material, naturally first upon 

 those parts which sooner or later are to become superfluous. 

 This applies eminently to the tail, which represents a consider- 

 able amount of " edible " matter, and also to that portion of the 

 skin which still covers the fore -limbs. The elements of the 

 cutis are resorbed, thereby thinning the skin ; and consequently 

 the limbs break through earlier in fasting than in well-fed 



' Arch. mikr. Anat. xxix. 1887, p. 1. 



