50 ANIMAL LIFE PAST AND PRESENT. 



function is, however, to maintain the balance of the 

 body in the water ; a fish which has lost one of these 

 fins falling over to the opposite side. It will be 

 observed from Fig. 16, that the pectoral fin of a Perch 

 (as well as of most of our existing fishes) consists of a 

 number of rays spreading out in a fan-like manner 

 from the point of attachment to the body. A totally 

 different arrangement obtains, however, in the pectoral 

 fin of the extinct fish represented in Fig. 2, p. 5. Here 



FIG. 1(5. The Common Perch. 



it will be seen that the fin consists of a central lobe 

 covered with scales, from the edges of which the 

 fin-rays project as a deep fringe. This more primitive 

 type of fin is indeed very common among the extinct 

 fishes of the Palaeozoic rocks, and still persists in 

 the Baramunda of the Queensland rivers, a figure of 

 which is given in the chapter on " Mail-Clad Animals." 

 The more important median fins are the dorsal on the 

 back, and the anal in front of the tail. In many 

 fishes (Figs. 2 and 16) there are two dorsal (ins, one in 



