FINS. XI 



the second almost entirely of rays as in the red mullet (plate viii), or con- 

 sisting of soft rays only as in the rock -ling (plate lxxxix) ; or the fin may 

 be divided into three parts as in the cod-fish (plate lxxviii) and many other 

 gadoids. The anterior portion of the dorsal fin may be in the form of free 

 spines as in some of the sticklebacks (plate lxviii), or the free spines may 

 be modified into tentacles as in the angler (plate xxix), or into an adhesive 

 apparatus as in the sucking-fish (plate xxxix) . Or the posterior portion of 

 the dorsal fin may be present in the form of free rays as in the tunny 

 (plate xxxv), or it may be simply a fold of skin containing fat as in the 

 salmon (plate ex), which in some conditions of embryonic or early life may 

 be observed to contain fin rays as in certaiu salmonoids and siluroids. When 

 spines are present in the dorsal fin they are usually in its anterior, and rarely 

 in its posterior portion ; but in one British form, the viviparous blenny, a 

 few are present with articulated rays anterior and posterior to them (plate 

 lxi). This fin may likewise unite with the caudal, the latter being continuous 

 with the anal, as observed in eels (plate cxlii). The spines and rays of 

 which fins arc composed can bo erected or depressed at will, while some 

 osseous and frequently posteriorly serrated rays or spines have a peculiar 

 joint at their base, which prevents their being depressed in a direct line, as 

 in the trigger fish (plate cxlvi). 



The pectoral or breast fin may be absent as in some pipe-fishes, marine- 

 eels, &c, but when present is subject to many modifications and assists in the 

 performance of functions which at first sight would hardly appear to be 

 among its duties. Its position is behind the gill-openings, but its form 

 differs ; thus among the Pediculati, as the angler, it possesses a sort of arm 

 due to prolongation of the carpal bones, enabling its possessor to employ 

 the organ as a foot or arm, and thus adapting it for moving about at the 

 bottom of the sea ; similarly some of the goby family in tropical countries 

 are enabled to use this fin for progression over the moist mud. Or the 

 pectoral fin may be considerably elongated as in the flying-fish (plate exxviii), 

 by which it can be used as a parachute in order to pass through the air. 

 Portions of the fin may likewise be modified, thus some free rays may exist 

 at or near the base of the pectoral fin, and subserve the function of feelers 

 as in the mango-fish and other polynemi, or these free rays may be shorter and 

 thicker as in the gurnards (plate xxii), when they become not only useful 

 as a tactile organ but also for progression. In some forms this difference in 

 the character of the rays also exists when forming an undivided fin, thus in 

 the pectorals of blennies, as in the common shanny (plate lx, fig. 2), there are 

 thirteen rays, the upper seven of which are shorter and more elastic than the 

 lower six. Under certain circumstances these upper- rays are useful in 

 respiration, as in cases wherein a deficiency of air exists in the water, when 

 they are constantly in motion, sending a current towards the gills.. In very 



