CHAPTER XXIX 

 THE STRUCTURE AND ACTIVITIES OF FISHES 



FISHES are rather easy to study since specimens can be ob- 

 tained in fish markets for examination in the laboratory. The 

 common perch is perhaps the best species because of its conven- 



FIG. 155. Diagram of a fish (perch) with parts named. 



a, anal fin ; br, branchiostegal rays ; ch, cheek ; cp, caudal peduncle ; dl, 

 spinous dorsal fin ; d2, soft dorsal fin ; d2r, rays of second dorsal fin ; d2s, 

 spines of second dorsal fin ; dcp, depth of caudal peduncle ; dp, depth (of 

 body) ; e, eye ; id, insertion of dorsal fin ; io, interopercle ; md, lower jaw, or 

 mandible ; mx, maxillary ; n, nose, or snout ; np, nape ; o, opercle ; p, pectoral 

 fin ; pmx, premaxillary ; po, preopercle ; so, subopercle ; v, ventral fin. 

 (After Forbes.) 



ient size and general distribution. Every one who has ever had 

 the opportunity has " gone fishing," and knows something about 

 the differences between different species. A great many peculiar 

 fishes, however, live in the sea or are confined to restricted parts 



271 



