INTRODUCTION. 9 



The caudal fin or "tail-fin": Like the dorsal fin (or 

 fins) the caudal is subject to great variation in shape; 

 in some fishes being slightly or deeply-forked, in others 

 rounded, in others again, produced into a fine point (or 

 even into filaments), while there are all imaginable modi- 

 fications of these and other shapes. In some cases, the 

 caudal fin is joined to both the dorsal and anal fins ; the 

 three combined, making one continuous fringing fin. 

 Familiar instances, amongst many, in which this occurs, 

 are the Eels, the common Catfishes, the Black Sole and 

 the Australian Rockling.* The caudal fin is most highly 

 forked in the Mackerels and other closely allied swift- 

 swimming fishes; in fact a highly- forked tail, may be 

 taken pretty generally as an indication of high speed. 



In the accompanying illustration, are shown the tail- 

 fins of a few of our fishes; while if the reader looks 

 through the illustrations of fishes which occur in the 

 following pages, the great diversity of form in this 

 appendage will be still more apparent. 



The caudal fin is of the highest importance to a fish ; 

 its function being to assist in propelling and steering the 

 latter through its aquseous surroundings. 



The pectoral fins : These fins represent in the fishes 

 the forelegs or arms of mammals and the wings of birds. 

 They are very important to a fish, assisting it very 

 materially (a) in maintaining its equilibrium, and (b) in 

 guiding it through the water; while in many fishes they 

 are often used within narrow limits as a means of pro- 

 pulsion. Like the dorsal and caudal fins, the pectorals 

 are subject to great modification in shape. More com- 

 monly, they are either simply rounded or pointed; but 

 sometimes, some of the rays are produced into fine fila- 

 ments, or into long finger-like processes. In the Gur- 

 nards and Threadfins some of the pectoral rays are de- 

 tached from the main fin ; in the first instance being 

 finger-like and adapted for "walking" along the bottom; 

 while in the latter, they are more or less prolonged into 

 fine hairs ; their function being to act as tactile organs 

 (organs of touch). 



* In some of these there is really no true caudal fin. 



