^'V 



300 THE MECHANICAL TUNCTIONS. 



are more especially useful for steadying the body, arc long- 

 est in those fishes which inhabit the most stormy seas. The 

 most voracious tribes, which incessantly pursue their prey, 

 are furnished with most pow^erful muscles, and possess the 

 greatest means of rapid progression. On the other hand, 

 many of the more pacific, and weaker species are studiously 

 guarded by a dense and hard integument, serving as a shield 

 against the attacks of enemies, and often armed v^ith sharp 

 points, which are sufficient to repel the most daring assail- 

 ant. The Balisies is covered with scales of singular hard- 

 ness, closely set together, and frequently having rough 

 edo-es. The Ostrucioii, or trunk fish, instead of these scales, 

 is provided wnth a kind of coat of mail, composed of osseous 

 plates, curiously joined together, like a tesselated pavement, 

 and reminding us of the arrangements we have seen adopted 

 in the calcareous coverings of the echinida. 



Some of the cartilaginous fishes are, in like manner, pro- 

 tected by calcareous plates, appended to the integuments. 

 There is a row of plates of this kind, of a quadrangular 

 shape, which passes along the middle of the back in the stur- 

 geon: and the whole body of the Ostracion, or Trunk-fish, 

 is covered with osseous scales. All these have no imme- 

 diate relation to the skeleton, but are apparently remnants 

 of inferior types, of which one of the prevailing characters 

 is the external situation of the protecting organs. 



Diodons and Tetrodons are remarkable for being provided 

 with the means of suddenly assuming a globular form, by 

 swallowing air, which, passing into the crop or first stomach, 

 blows up the whole animal like a balloon. The abdominal 

 renion beino; thus rendered the lightest, the body turns over, 

 the stomach becoming the uppermost part; and the fish floats 

 upon its back, without having the power of directing itself 

 durino: this state of forced distention. But it is while lying 

 thus bloated and passive, at the mercy of the waves, that this 

 animal is really most secure; for the numerous spines, with 

 which the surface of the body is universally beset, are raised 

 and erected by the stretching out of the skin, thus present- 



