CONCERNING TADPOLES 183 



that of a parrot, but blunter. They break up tiny particles of 

 food by a rasping action like that of snails. This formidable 

 armature is used to demolish convervae and other vegetable 

 matter, or, when obtainable, the dead bodies of their com- 

 rades or other creatures which have fallen by the way. 



The eye now shows its first signs of being, making its ap- 

 pearance as a ring of pigment just under the skin. Soon after 

 this, four slit-like apertures pierce the walls of the upper 

 end of the gullet, and their margins speedily become folded 

 to form internal gills, and in proportion as they develop, 

 so the external gills, always a source of danger, decline. 



A stage is now reached in the development of this larva 

 answering to the condition of the adult fish ; that is to 

 say, it breathes by internal instead of external gills. The 

 growth of the internal gills is accompanied by the develop- 

 ment of a backward growth of the skin of the head so as to 

 enclose these gills within a chamber. Towards the end of 

 the fourth week the hinder edges of these folds of skin 

 merge, or fuse, with the body wall, leaving a spout-shaped 

 opening on the left side of the body, and through this the 

 water taken in at the mouth, after having bathed the 

 gills, is passed. Thus is breathing carried on. 



Thelarvalstagehas now ended, and the "tadpole" stage has 

 begun. By much feeding the body, inky black and spangled 

 with gold, has become large and round, and the tail has 

 greatly increased in length and thickness, forming, as in the 

 fish, a powerful swimming organ. Meanwhile the suckers 

 bordering the mouth have decreasedin size andarehttleused. 

 At the base of the tail two little buds have made their appear- 

 ance. These are the rudiments of the hind-legs : by about 

 the seventh week they have become divided into segments or 

 " joints," and a week later the toes make their appearance. 

 The fore-limbs have reached a similar stage of growth, but 

 as yet they lie hidden, folded up within the gill chamber. 



