FISHES. 115 



in part within the skull. In structure it is by no 

 means so complicated as in the quadrupeds and 

 other animals that live in the air. Some genera, as 

 the Rays, have the external orifice very small, and 

 placed on the upper surface of the head ; but in 

 others there is no external opening whatever. 



The food of these animals is almost universal in 

 their own element. Insects, worms, or the spawn 

 of other fish, sustain the smaller tribes ; which, in 

 their turn, are pursued by larger foes. Some feed 

 on mud and aquatic plants, but by far the greater 

 part subsist on animal food alone ; and they are so 

 ravenous as often not to spare those of their own 

 kind. Those that have the most capacious mouths 

 pursue nearly every thing that falls in their way, 

 and frequently meet in fierce opposition. The fish 

 with the widest mouth is usually victorious, and he 

 has no sooner conquered than he devours his anta- 

 gonist. Innumerable shoals of some species pur- 

 sue those of another through vast tracts of the 

 ocean ; from the vicinity of the pole sometimes 

 even to the equator. In these conflicts, and in this 

 scene of universal rapine, many species must have 

 become extinct had not nature accurately propor- 

 tioned their means of escape, their production, and 

 their numbers, to the extent and variety of the 

 dangers to which they are exposed. The smaller 

 species are consequently not only more numerous 

 and prolific than the larger, but their instinct im- 

 pels them to seek food and protection near the 

 shore, where, from the shallowness of the water, 

 many of their foes are unable to pursue them. 



I 2 



