THE FISHES 275 



bones, the ribs, with other spiny bones to which the unpaired fins are attached. 

 The paired fins are attached to the spinal column by two collections of bones, 

 known respectively as the pectoral and 'pelvic girdles. The bones serve in 

 the fish for the attachment of powerful muscles, by means of which loco- 

 motion is accomplished. 



The Egg-laying Habits of the Bony Fishes. — The stickleback 

 has the rather curious habit (for a fish) of nest building. The nest 

 is attached to waterweeds or a submerged stick. It is almost 

 circular in outline, and in the case of the common stickleback is 

 about two inches in diameter. A hole in the top gives access to 

 the interior. In this nest the female deposits her eggs, which are 

 then guarded by the male until the young hatch out. The fresh- 

 water sunfish also has the habit of nest building, its nest being 

 scooped out in the sand of the lake or river bed. 



The eggs of most bony fishes are laid in great numbers at the 

 time of spawning. This number varies from a few thousand in 

 the trout to many hundreds of thousands in the shad and several 

 millions in the cod. The time of egg laying is usually spring or 

 early summer. Usually the eggs are left to develop by themselves, 

 sometimes attached to some submerged object, but more frequentty 

 free in the water. They are exposed to many dangers, and both 

 eggs and developing fish are eaten, not only by birds, fish of other 

 species, and other water inhabitants, but also by their own relatives 

 and even parents. Consequently a very small percentage of eggs 

 ever reach maturity. 



The Relation of the Spawning Habits to Economic Importance of 

 Fish. — The spawning habits of fish are of great importance to us 

 because of the economic value of fish to mankind, not only directly 

 as a food, but indirectly as food for other animals in turn valuable 

 to man. Many of our most desirable food fishes, notably the 

 salmon, shad, sturgeon, and smelt, pass up rivers from the ocean to 

 deposit their eggs. The salmon is said to travel thousands of 

 miles, swimming against strong currents much of the way, leap- 

 ing rapids and falls, in order to deposit her eggs in suitable 

 localities, where the conditions of water and food are requisite, 

 and the water shallow enough to allow the sun's rays to warm 

 the water suflSciently to cause the eggs to develop. At the 



