363 



Chapter VIL 



FISHES. 



In reviewing the series of animals which compose 

 each great division of this kingdom of nature, we 

 constantly find that the simplest structures and 

 modes of progression are those belonging to the 

 aquatic tribes. Among vertebrated animals, the 

 lowest rank is occupied by Fishes, a class compre- 

 hending an immense number of species, which are 

 all inhabitants of the water, which exhibit an end- 

 less variety of forms, and open to the physiologist a 

 wide field of interesting research. We cannot fail 

 to perceive, on the most cursory glance, the beau- 

 tiful adaptation of the form and structure of all 

 these animals to the properties of the element in 

 which they are destined to reside. In order that 

 the fish might glide through the fluid with the least 

 resistance, all its vital organs have been collected 

 into a small compass, and the body has been re- 

 duced into the shape of a compact oval, compressed 

 laterally, and tapering to a thin edge, both before 

 and behind, for the purpose of readily cleaving the 

 water as the fish darts forward, and also of obviating 

 the retardation which might arise from the reflux of 

 the water collected behind. With a view to dimi- 

 nish friction as much as possible, the surface of the 

 body has been rendered smooth, and the skin im- 

 pregnated with oil, which defends it from injurious 

 impressions, and at the same time prevents the 

 water from penetrating into its substance. 



