ix. 2 BODY FORM OF FISHES 249 



which there are several different sorts; Lophius piscatorins (Fig. 150) 

 is common in British waters. It is much flattened, with a huge head 

 and mouth and short tail. It 'angles' by means of a dorsal fin, modified 

 to form a long filament with a lump at the end, which hangs over the 

 mouth. Swimming, though vigorous, is slow, and protection (both for 

 attack and defence) is obtained by sharp spines, protective coloration, 

 and flaps of skin down the sides of the body, which break up the 

 outline. There is even a special fold of pigmented skin over the lower 

 jaw, serving to cover the white inside of the mouth. 



Other anglers are the star-gazers, Uranoscopiis of the Mediter- 

 ranean and Astroscopes from the Western Atlantic seaboard. Their 

 lure is a red process attached to the floor of the mouth and they lie in 

 wait buried in the sand, with the mouth opening upwards and only 

 the eyes showing. The colour is protective, there are poison spines, 

 and in Astroscopus there are electrical organs located near the most 

 vulnerable spot, the eyes, and formed from modified eye-muscles 



(P- 253)- 



Other fishes abandon the swift-moving habit for the protection 

 afforded by the development of heavy armour, such as that of the 

 trunk-fish (Ostracion) and the globe-fish (Chilomycterus) (Fig. 149). 

 Special spinous dorsal rays, such as those of the sword-fish {Xiphias) 

 may be developed, without loss of the swift-moving habit; indeed 

 these fish are among the fastest swimmers. There are many groups in 

 which an elongated body form like that of the eel has been developed. 

 In Anguilla itself this is associated with the habit of moving over land. 

 The Syngnathidae, sea-horses and pipe-fishes, no longer swim with 

 the typical fish motion but by passing waves along the dorsal fins. 

 The long and often grotesquely cut-up body form gives a strong 

 protective resemblance to the weeds among which they live and on 

 which they feed. The tail of the sea-horses has lost its caudal fin and 

 is used as a prehensile organ, being wrapped around the stems of 

 sea-weeds for attachment. 



Evidently the mastery that the Actinopterygii have acquired in the 

 water has depended to a large extent on the freedom given by the use 

 of the air-bladder as a hydrostatic organ. This gives special interest to 

 the question of how this use first began. If we are right in supposing 

 that the bladder was first a respiratory diverticulum of the pharynx, 

 can we suppose that its value as a hydrostatic organ depended on any 

 exertion of effort of the fishes, or was this a case in which those born 

 with the organ better developed found themselves with an advantage ? 

 It would seem that the latter orthodox Darwinian interpretation is the 



