2 4 2 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



with it are mucous tubes and other pores. It is well supplied 

 with nerves and it has been thought by some to be an organ 

 of sense, perhaps some sense that man does not possess and 

 therefore does not understand. It is closely associated with 

 the ear-sac, and possibly has some similar function, that is, 

 of determining vibration waves. 



Most fishes are colored in such a way that they are hard to 

 detect in their natural environment, and are thus protected, 

 in a measure, from their natural enemies. Some show bright 

 colors only at breeding time while still others are beautifully 

 and brilliantly colored at all times. 



The skeleton consists of the many bones composing the skull 

 and jaws, the shoulder girdle, the backbone with a varying 

 number of ribs and intermuscular bones, and the bones sup- 

 porting the fins. Most of these bones are comparatively soft 

 having little lime in them. Indeed, in many cases they are 

 mere cartilage. The small free intermuscular bones lie im- 

 bedded in the flesh, and when abundant materially lessen the 

 value of the fish for food. 



The air-bladder or swim-bladder is a characteristic struc- 

 ture that is found in many fishes. In the garpike, bowfin 

 and the lung-fishes it is connected with the esophagus and is 

 used as a lung for breathing. In others it is joined through 

 the modified bones of the neck to the organ of hearing. Its 

 normal function seems to be hydrostatic, that is, it helps to 

 keep the fish of the same specific gravity as the water by the 

 absorption or secretion of gas. 



Most fishes lay eggs which are fertilized outside of the body 

 by the male pouring the milt, or spermatozoa, over them as 

 they settle into the gravel or other places where they are to 

 develop. A few make more or less elaborate nests where the 

 eggs are protected until they hatch. These usually produce 

 fewer eggs than those that make no provision for the care of 

 their eggs. Some of the perch-like kinds and a few others 

 retain the eggs in the body until they hatch, and thus produce 

 living young. 



Fish Culture. Many of our best food-fishes occur in seem- 

 ingly inexhaustible numbers. When we read of shoals of 



