ii8 A HISTORY OF FISHES 



forward as a whole, the movement of the lower jaw pulHng it 

 away from the head. Included in the same order is a remark- 

 able deep-sea fish to which the name of Stylophorus (referring 

 to the whip-like prolongation of the lower lobe of the caudal 

 fin) is applied. This fish was first described in 1791, but it is 

 only in recent years that the discovery of well-preserved speci- 

 mens has made it possible to elucidate its anatomy. The 

 mouth is extraordinarily protractile, and when protruded 

 appears at the end of a long funnel-like pouch (Fig. 49D). A 

 point of particular interest Hes in the fact that the diflferent 

 parts of the jaws are so arranged that in order to thrust the 

 mouth forward the fish must throw the head upwards and 

 backwards. "We may imagine this Httle fish," writes Dr. 

 Regan, "not more than twelve inches long, swimming in the 

 Atlantic two or three hundred fathoms below the surface, 

 peering ahead into the semi-darkness, and stealthily approach- 

 ing its prey, which must be quite small, accurately judging 

 when it is within striking distance, and then suddenly throw- 

 ing back its head and thrusting out its mouth to eflfect the 

 capture." 



Among the Flat-fishes the characteristic asymmetry is 

 extended to the mouth and jaws in many forms. In Psettodes, 

 the most primitive member of the group, the jaws are more or 

 less of the same size, and the teeth almost equally developed on 

 the coloured and on the bhnd side. The same condition is 

 found in the Halibut {Hippo glossus) and in certain other species, 

 which are in the habit of leaving the bottom and swimming 

 strongly in active pursuit of other fishes. In other forms, 

 however, of which the Plaice [Pleuronectes) and the Dab 

 [Limanda) will serve as examples, the mouth is much twisted, 

 being more developed and armed with a greater number of 

 teeth on the lower or bhnd side. This modification is con- 

 nected with different habits, these fishes being less active, 

 keeping constantly at or near the bottom, and feeding mainly 

 on shell-fish and other ground-Hving invertebrates. In the 

 Soles [Soleidae) and Tongue Soles {Cynoglossidae) , which are 

 even more speciahsed, the jaws and teeth are extremely feeble 

 on the upper side of the fish, and the mouth is twisted almost 

 completely on to the under surface. The Sole {Solea) is a 

 retiring fish, burrowing into the sand and seldom moving, 

 except at night. It is provided with special sensory organs on 

 the lower surface of the head, and, according to Dr. Cunning- 

 ham, hunts for worms or shrimps by tapping the ground gently 



