THE FISHES 



273 



the stickleback are small and evidently useful for seizing and holding prey. 

 This fish, like many other specie's, is a hunter and uses the teeth as weap- 

 ons of offense as well as for defense. How are the teeth of the stickleback 

 adapted to their functions ? The tongue in most fishes is wanting or very 

 slightly developed. 



Gill Rakers. — If we open wide the mouth of any large fish and look in- 

 ward, we find that the mouth cavity leads to a funnel-like opening, the 

 gullet. On each side of the gullet we can see the gill arches, guarded on 

 the inner side by a series of sharp pointed structures, the gill raker a. In 

 some fishes in which the teeth are not well developed, there seems to be a 

 greater development of the gill rakers, which in this case are used to strain 

 out small organisms from the water which passes over the gills. Many 

 fishes, as the shad and menhaden, make such use of the gill rakers. 



Digestive System. — The gullet leads directly into a baglike stomach. 

 There are no salivary glands in the fishes. There is, however, a large liver, 

 which appears to be used as a digestive gland. This organ, becau.se of the 

 oil it contains, is of considerable economic importance. Many fishes have 

 a number of pocketlike outgrowths from the intestines. These structures, 

 called the pyloric cceca, are believed to secrete a digestive fluid. The intestine 

 ends at the vent, which is usually located on the ventral side of the fish, 

 immediatel}'' in front of the anal fin. 



Anatomy of the carp ; 6r, branchiae, or gill openings ; c, heart ; /, liver ; vn, swimming 



bladder ; d, intestine. 



Swim Bladder. — An organ of unusual significance, called the swim 

 bladder, is connected with the digestive tract in front of the stomach. In 

 young fishes of many species this connection is a tube, which in some forms 



hunter's BIOL. 18 



