VALUE OF SNAKES 



543 



around Ceylon. It seems likely that the most perfect pearls are 

 due to the growth within the mantle of the clam or oyster of cer- 

 tain parasites which are stages in the development of a fluke worm. 

 The irritation thus set up 

 in the tissue causes mother- 

 of-pearl, the substance 

 that lines the interior of 

 the shell, to be deposited 

 around the source of irrita- 

 tion, with the subsequent 

 formation of a pearl. 



The pearl-button in- 

 dustry in this country is 

 largely dependent upon 

 the fresh-water mussel, 

 the shells of which are 

 used. This mussel was 

 being so rapidly depleted 

 that the national govern- 

 ment has worked out a 

 means for its artificial 

 propagation. 



Usefulness of the toad. 

 The toad is of great eco- 

 nomic importance to man 

 because of its diet. No 

 less than eighty-three 



species of insects, mostly injurious, have been proved to enter into 

 the toad's diet. A toad has been observed to snap up 128 flies 

 in half an hour. Thus it could easily destroy very many insects 

 during a day and do an immense service to the garden during the 

 summer. Toads also feed upon slugs and other garden pests. 



Value of snakes. Probably the most disliked and feared of all 

 animals are the snakes. This feeling, however, is rarely deserved, 

 for, on the whole, our common snakes are beneficial to man. The 

 black snake, gopher snake, and milk snake feed largely on 

 injurious rodents (rats, mice, etc.), the green garden snake eats 



Wright Pierce 



Chuckwalla — a stout-bodied lizard of the deserts 

 of southwestern United States. It feeds on the buds 

 and flowers of plants. Its flesh is used by some 

 people for food. 



