436 ZOOLOGY. 



The ear has no external opening, being completely encased 

 in bone. Xearly parallel with the line of the back extends 

 a continuous row of yellow spots marking the lateral line 

 •(Fig. 399, L), along which are found the pore-like open- 

 ings of the so-called muciparous gland;. 



All fish haye fins of two kinds— unpaired and paired ; the 

 latter, four in number, correspond to the limbs of other Ver- 

 tebrates. The unjiaired fins are first developed on a contin- 

 uous median flap of integument, which extends along the 

 back, around the tail, and on the underside as far forward as 

 the anus ; cartilaginous or bony rays are developed in it as a 

 support. In the adult fish the fold is generally disi- 'ntinu- 

 ous, being usually separated into three distinct fin? — lioisal, 

 •caudal, and anal ; the dorsal fin is frequently, tlie anal fin 

 sometimes subdivided. The fin-rays are (1) either simple 

 pointed rods, or (2) jointed and branching. All the rays of 

 the caudal fin, and the posterior rays of the dorsal and anal 

 fins, are branching. In some Malacopterygians all the rays 

 are branching ; in many, however, the first ray is simple in 

 the dorsal and anal fins, while fishes like the perch and cun- 

 ner are distinguished by having several or many of the an- 

 terior rays of the dorsal and anal fins simple and pointed. 

 In the cunner half the rays of the dorsal and the first two of 

 the anal fin are simple. 



The pectoral fins are attached to the side of the body and 

 are large and rounded. The ventral fins lie further back 

 near the median ventral line ; they are smaller than the pec- 

 torals. The position of the veatrals varies in different fi^h. 

 and is much used in classification. The anus lies immedi- 

 ately in front of the anal fin. 



The body is covered by scales, which overlap one another 

 from before backward ; tlieir free edges are rounded and 

 smooth, hence they are called cycloid. These scales, as in 

 all Teleosts. are ossifications of the underlying cutis, and are 

 covered by tlie epidermis ; they were formerly wrongly sup- 

 posed to be epidermal structures. 



To dissect a perch the side-wall of the mouth must be re- 

 moved, then the gill-cover ; study the arrangement of the 

 gills. Next make an incision along the median ventral line 



