OF THE BRITISH ISLANDS. 75 



tion or foreshadowing of this Eel-like continuity of the fins 

 in question is met with in those typical Cod-species in 

 which as many as three dorsal and two anal fins take the 

 place of the short single or double dorsal, and single anal 

 fin developed in ordinary fishes. A highly remarkable, 

 but as yet apparently unexplained physiological function is 

 associated with the first dorsal fin in the genus Motella. 

 As may be observed of examples confined in the tanks of 

 an aquarium, this fin is sunk within a deep groove, above 

 which, although of a considerable length, it is elevated to a 

 very small extent. During life, even while the fish is 

 otherwise quiescent at the bottom of the water, this fin 

 is in a constant state of vibration, undulating from before 

 backwards, much after the manner of the dorsal fin of the 

 Pipe-fish (Syngnathus) when used for locomotion, but more 

 rapidly and continuously. The Rocklings are litoral species, 

 that in a state of nature usually lie hid beneath stones, or 

 among the tangled masses of sea-weed that line the shore ; 

 and it would seem by no means improbable that the un- 

 dulations of this fin, in connection with its groove, subserve 

 the purpose of bringing fresh streams of water to the 

 vicinity of the respiratory organs, the fish being thus 

 enabled to live in small holes and crannies, that would 

 otherwise be too stagnant for its healthy existence. The 

 commonest form, known as the Five-bearded Rockling 

 {Motella musteld), is very plentiful around our coasts. It is 

 distinguished, as its name implies, by the possession of five 

 cirrhose appendages or barbels, four of which are developed 

 from the upper and one from the lower lip. Its ordinary 

 length is about twelve inches, and its colour in life is a rich 

 chestnut or olive brown, with bronze reflections. A larger 

 and yet more handsome species is the Three-bearded 

 Rockling {Motella tricirratd), attaining to a length of as 



