Ranidae 



available. Thus these tadpoles act as scavengers and dispose 

 of dead fish, or dead tadpoles even, that otherwise would become 

 a menace to the living creatures of the pond. 



On the left side of the tadpole is a conspicuous opening: the 

 breathing-pore. (See Fig. 283.) The breathing is done by means 

 of internal gills on each side of the throat, in a position like that 

 of a fish's gills. They are concealed, however, by the outer skin. 

 (Fig. 280.) This is the fold of skin which grows back from the 

 sides of the head in the young tadpole and covers the external 

 gills. 1 There are three sets of these internal gills on each side. 

 They are feathery tufts extending into cavities between the walls 

 of the throat and the outer skin of the sides of the head. These 

 cavities, or gill-chambers, are connected with each other by 

 a passage underneath the skin of the throat. (See Fig. 280.) 

 Alternating with the tufts of gills, there are three openings 

 in the throat-wall. These openings (gill-slits) connect the throat 

 and mouth with the gill-chambers at the sides of the head. Water 

 is constantly passing in at the mouth and nostrils, through the 

 gill-slits into the gill-chambers, over the gills, and out at the breath- 

 ing-pore. The water of the gill-chamber on the right passes into 

 the gill-chamber on the left, and thence out of the breathing- 

 pore on the left side. 



One important way in which the tadpole is fitted to cope 

 with the difficulties of his life is his power of reproducing the tail, 

 should a hungry fish or other enemy bite it off. When you col- 

 lect tadpoles for the aquarium, do not collect and put in with 

 them the giant diving-beetles or any other of the tadpole's enemies. 

 If you do so, on the first morning after the aquarium is arranged 

 the beetles will be looking very hearty and the tadpoles will be 

 scared, wobbling, tailless creatures, which demand quick rescue 

 before the beetles complete their destructive work. However, 

 if the beetles are removed, the tadpoles soon recover their assur- 

 ance, and in a very few weeks their waving filmy tails are nearly 

 as long as they were before the disaster. 



The lateral-line organs are easily made out because of the 

 large size of the tadpole. 3 



On the second day of our observation (July 4th) the mouth is 

 beginning its transformation. It is much wider, and as it is con- 



1 See Leopard Frog, Fig. 211. 



3 For figure, and discussion of lateral-line organs, see p. 6. 



236 



