430 ZOOLOGY. 



The ear has no external opening, being completely encased 

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

 a continuous row of yellow spots marking the lateral line 

 (Fig. 3'JU, L), along which are found the pore-like open- 

 ings of the so-called nuiciparous glands. 



All fish have fins of two kinds unpaired and paired ; the 

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

 tebrates. The unpaired 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 discontinu- 

 ous, being usually separated into three distinct fins dorsal, 

 caudal, and anal ; the dorsal fin is frequently, the 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 dinner 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 ventrals varies in different fish, 

 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 ; their 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 the 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 



