AMPHIBIANS. 209 



one days, but they often remain dormant for many weeks. 

 The tadpoles in their early days are all alike, though in 

 subsequent stages they exhibit marked differences according 

 to their Frog or Newt parentage. All have a large round 

 head, no body to speak of, but a flattened tapering tail, which 

 is used as a propeller. Under the chin is a pair of processes 

 forming a sucker by means of which they anchor themselves 

 to any convenient object, and they generally associate in 

 clusters while very young. When first hatched, the tadpole 

 is still in a semi-embryonic condition having neither eyes, 

 ears, nor breathing apparatus, respiration being effected chiefly 

 through the skin ; in about four days the organs just named 

 make their appearance, while on each side of the neck there 

 may be seen a small knob from which there soon issues a 

 pair of branching gills forming a frill (larger in Newt- than in 

 Frog-tadpoles). These, as well as the whole of the tail, are 

 semi-transparent, and if the tadpole be placed in the micro- 

 scope, the action of the heart (which consists of two chambers 

 only), can be plainly seen, as well as the blood with the large 

 oval corpuscles coursing through the gills, and the capillaries 

 in the tail. These vessels all arise from a large artery running 

 along the centre of the tail, and return their contents into a 

 vein parallel to the artery. The gills are covered on the 

 outside with cilia (minute vibrating hairs), which by their 

 action produce currents in the surrounding water and so 

 bring up a constant supply of fresh water to aerate the blood 

 coursing through them. At first the tadpole is nourished by 

 the remains of the yolk-sac inside its body, but that is 

 quickly absorbed and it then begins to feed voraciously on 

 confervoid algae, etc. The lips are soft at first; later on they 

 are produced into a kind of beak, provided with a horny 

 sheath, of great use in dividing the food. The gills reach 



