THE STUDY OF AMPHIBIANS 



begins to feed on minute unicellular plants and on the particles 

 of decaying plants and animals. 



The First " Tadpole " Stage. About a month after hatching, 

 what is strictly called the first true tadpole stage is seen. A 



FIG. 42. An older stage, a few 

 days after hatching, seen from 

 below. The external gills (EG) 

 are now well developed. The 

 adhesive gland (AG) has been 

 divided into two. The mouth 

 (M) has a pair of horny jaws, 

 and the lips bear minute horny 

 papillae. 



FIG. 43. A later stage shows the intestine (INT) coiled 

 like a watch-spring, the rudiments of the hind-legs 

 (HL) as a pair of small papillae at the root of the tail 

 in front of the cloacal aperture (CL), the spout-like 

 opening or spiracle (SP) on the left side by which 

 the water, taken in by the mouth and passed out 

 through the gill-clefts (GC) into the gill-chamber, 

 regains the exterior. The adhesive glands (AG) 

 behind the mouth (M) are now very small. The 

 position of the two-chambered fish-like heart is 

 indicated (H). 



fold of skin has grown over the external gills, forming a gill- 

 chamber, with a single aperture (or spiracle) to the left-hand side. 

 The enclosed gills dwindle away and are replaced by a second 

 set, often called " internal " gills, consisting on each side of four 

 sets of small branched threads supported on four gill-arches. The 

 general arrangement may be made clearer by examining any 

 common bony fish, such as a haddock or a trout, which shows a 



