FISHES 



87 



Shore- Hunters. — Widely distributed along the tropical and 

 temperate coasts of the world are to be found the Gobies, which 

 constitute a family of small carnivorous species. Some of these, 

 known as Mud- Skippers, abound in the 

 I ndo- Pacific region and are represented on 

 the west coast of Africa, one extremely 

 common kind from the former area being 

 Periophthalmus Kcelreuteri. This, like the 

 other allied species, instead of keeping to its 

 own proper element, makes a hunting-ground 

 of the shore between tide-marks, especially 

 when it is muddy or uneven, and littered 

 with brown sea-weeds or mangrove roots. 

 Progressing by a series of hops, effected by 

 means of the tail and strong, paired fins, it 

 pursues relentlessly small crabs and other 

 invertebrates, and such insects as mosquitoes 

 have been found in its stomach. The large 

 protruding eyes are capable of very free 

 movement, and an investigation of their 

 structure has shown that they are as useful wedge-shaped structure bebw is 



, the ventral fin. 



on land as in the water. 



Insect- Eaters. — Insects are included in the diet of the last- 

 named fish, and it is, of course, a common thing to see fish rise 

 at "flies" which fall into the water, but a much more interesting 

 case is that of the Beaked Chelmon (Chelmon rostratus), an in- 

 habitant of Indian rivers and estuaries. It possesses a long 

 tubular snout, from which it is said to be able to eject drops of 

 water for a distance of several feet with considerable force, the 

 object being to knock into the water insects which have alighted 

 on vegetation near the edge. 



Use of Sense Organs. — Among the higher back-boned animals 

 cases have been cited where the senses of touch, smell, and sight 

 respectively are of importance in the detection or pursuit of prey. 

 Ducks, dog-like animals, and vultures may be mentioned as typical 

 instances. Fishes afford examples of all three cases, but it will 

 be convenient to postpone details till organs of sense are dealt 

 with in a later section. 



Fig. 368. — Cross-section through 



Electric Eel 



00, Electric organ, above which 



on either side are seen four masses 



of muscle (darkly shaded). The 



