FINS 65 



fins, as well as the outer rays of the pelvics, are converted into 

 stiff-pointed spines. Occasionally these spines are slender and 

 flexible, but they may always be readily distinguished from true 

 soft rays by the absence of joints or branches. 



Among the more generalised Bony Fishes the dorsal fin may 

 retain its primitive form as a long fringe along the middle line 

 of the back, especially in those species which use it as an organ 

 of locomotion (Fig. 28c). In all the Eels (Apodes) the dorsal 

 and anal fins are united with the caudal when this is present, 

 and in the Morays or Muraenas {Muraenidae) the skin covering 

 the fins is so thick that no trace of the rays is visible externally 

 (Fig. 83A). A peculiar conger-like Eel from the West Indies 

 {Acanthenchelys) is worthy of mention, in which the greater part 

 of the dorsal fin is supported by soft rays in the usual manner, 

 but in a small section near the tail these have been converted 

 into stiff spines. Examples of spines following soft rays are very 

 rare indeed, but the Viviparous Blenny or Eel Pout {Zoarces) 

 of our own shores provides another case. The elongate dorsal fin 

 occurs again in the Ribbon-fishes (Trachypteridae) , which swim 

 by means of wave-like movements of the body, aided by similar 

 undulations of the fin. In the Oar-fish {Regalecus), a large 

 oceanic species attaining a length of more than twenty feet, 

 this fin extends all the way along the upper edge of the com- 

 pressed body, and the first few rays are prolonged into rather 

 long filaments, each of which ends in a membranous flap 

 (Fig. 8d) . The fins are bright scarlet in colour, and the general 

 appearance of the head is not unlike that of a horse {cf. p. 429). 

 In the closely related Deal-fish ( Trachypterus) the form of the 

 dorsal fin in the young fish is remarkable, the first six or so of 

 the rays being produced into fine filaments more than four 

 times as long as the fish itself. These streamers are ornamented 

 with little membranous tags placed at intervals along their 

 length (Fig. 12 ib). Another member of the same tribe, known 

 as Velifer, derives its name from the relatively huge size of both 

 dorsal and anal fins (Fig. 28J). 



In the majority of Malacopterygians the primitive elongate 

 fin is either considerably reduced in size or is split up into two 

 or three separate fins. Thus, in the Herring {Clupea) and Carp 

 (Cyprinus) there is a single rather small fin in the middle of the 

 back composed entirely of soft rays, of which the first three or 

 four are simple and graduated in size, the remainder being 

 branched at their tips (Figs. 320; 43). Two extreme sizes of 

 single dorsal fin are encountered in the Feather-back [Notop- 



