XXII. FISHES 



The ordinary stickleback is a hardy fish easily kept in aquaria 

 in the schoolroom. It (or any other small fish, as the brook 

 minnow or goldfish) may be used in the following exercise.^ 



The Body. — The body of the fish runs insensibly into the head, the neck 

 being absent. Notice the long, narrow body. How is it adapted for the 

 method of hfe? Certain cells in the skin secrete mucus or slime. How 

 might the slimy surface of the body be useful to the fish ? If the fish is in 

 an aquarium with surroundings like that of its natural habitat, decide 

 whether the color of the fish is protective. 



The Appendages and their Uses. — The appendages of the fish consist of 

 paired and unpaired fins. The paired fins are four in number, and are be- 

 lieved to be homologous with the paired limbs of a man. Compare the fish 

 with the diagram in the book and locate the paired pectoral and pelvic fins. 

 (These are so called because they are attached to the bones forming the 

 pectoral and pelvic girdles. See page 275.) Find, by comparison with 

 th6 diagram, the dorsal, anal, and caudal fins. How many unpaired fins? 



The fins of a fish; A, dorsal; B, caudal; C, anal; D, pelvic; E, pectoral. 



The stickleback, as the name indicates, has the front dorsal fin so modi- 

 fied as to form a number of sharp spines. (There are five in the common 

 brook stickleback of New York state.) A careful study of a fi.^h in the 

 school aquarium will help to an understanding of the uses of the diflFer- 

 ent fins. Decide what part in the locomotion of the fi.sh is taken by the 

 caudal fin. Do the other fins function in forward movement? Which fins 

 are used in turning? In backing? Are any used in balancing? Do any 

 parts of the body play a part in locomotion ? 



1 See Hunter and Valentine, Manual, page 167. 



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