12 SALT-WATER FISHES 



of the malformed sea-breams so commonly caught in the 

 Plymouth district. 



It has already been pointed out that the specially modified 

 limbs of fishes, which we call "fins," are their most permanent 

 and enduring character. There is a persistence 

 about these organs of balancing and movement 

 that is not found in the limbs of higher vertebrates, and it 

 has been shown by somewhat cruel experiment * that if a fish 

 be deprived of its fins, it develops new ones in their place in 

 an incredibly short time. As Bashford Dean points out,t 

 those fins which look so important in profile dwindle to mere 

 lines when the fish is viewed end on, and this difi^erence shows 

 how admirably these animals are suited to rapid and un- 

 hindered progress through so dense a medium as water. 

 The fins of fishes are situated on the back, belly, and sides, 

 and they are either vertical and unpaired, or horizontal {i.e. 

 lateral) and paired. It seems probable that the latter are 

 chiefly useful in balancing the fish, aided no doubt by the 

 air-bladder, in a way that will be referred to later. The 

 vertical fins enable the fish to steer its course, the tail- 

 fin being most important in propelling the body forwards 

 or backwards. Different authors have preferred different 

 names for these fins. They agree in calling the fins on the 

 back the first and second " dorsal " respectively, and also 

 in naming the tail-fin the " caudal," and those immediately 

 behind the head " pectorals." It is in respect of the " anal " 

 fin (near the tail and below the fish) and " ventral " (the fin 

 before the anal) that some authors, Mr. Cunningham among 

 them, have elected to depart from the older nomenclature so 

 far as to reverse these names, or to name that which was 

 known as ventral " pelvic." What purpose can be served by 

 such confusing alterations it is difficult to conceive, and in the 

 present volume the older names of the fins have been retained. 



* See Regnard, La Vie dans les Eaux, p. 446. 

 t Fishes, Living and Fossil, p. 3. 



