THE ECONOMIC BIOLOGY OF VERTEBRATES 481 



rich in phosphorous compounds which most plants need. The 

 menhaden is much used for this purpose as well as for its oil. In 

 1913 over a billion of this species were taken, from which were made 

 6,500,000 gallons of oil and 90,000 tons of fertilizer. The total 

 weight of the year's catch of this one kind was more than the 

 weight of all the inhabitants of Greater New York. 



Cod liver oil is the easiest oxidized fat food in the world and 

 is valuable as a medicine. Isinglass, a fine quality of gelatine is 

 obtained from the air bladders of certain fishes. Glue is another 

 important product made from waste parts and bones of all sorts 

 of fish. 



Amphibia. The chief value of this group lies in its activities 

 in destroying harmful insects. Frogs, toads, and salamanders, 

 all unite in feeding upon them, the toad being especially useful 

 in this respect. To a very much less extent, frog legs are used 

 for food; frogs might much better be left to fight insects, rather 

 than be used for this purpose. 



Reptiles. We usually consider this group as useless or even 

 harmful, but with the rare exceptions of the venomous snakes, 

 the Gila monster, and a few man-eating crocodiles, this is not 

 true. Most snakes destroy either insects or harmful rodents, 

 though a few eat frogs, birds, or eggs. 



The turtle family not only destroys insects, but the tortoise 

 furnishes flesh and eggs as foods and tortoise shell for ornaments. 

 Alligators and crocodiles are not particularly valuable and oc- 

 casionally are dangerous. Their hides are sometimes made into 

 leather. 



Birds. The economic value of birds has already been mentioned; 

 they are our chief ally in the fight against our insect enemies; 

 they provide flesh and eggs for food; they supply feathers for 

 bedding and ornament; while their bright colors and sweet songs 

 have always made them cheerful companions and pets for man. 



In order to preserve these valuable members of society we can 



1. Learn to observe the laws made for their protection. 



2. Help restrain their enemies, the plume hunters, game hogs, 

 cats, red squirrels, black snakes, and certain birds such as Cooper's 



