DIODONS AND TETRODONS. 433 



have no immediate 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 region being thus rendered the 

 lightest, the body turns over, the stomach be- 

 coming the uppermost part ; and the fish floats 

 upon its back, without having the power of 

 directing itself during this state of forced dis- 

 tension. 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 presenting an 

 armed front to the enemy, on whatever side he 

 may venture to begin the attack. 



There is a numerous family of fishes, found 

 in the seas of India, so constructed as to be able 

 fro crawl on land to some distance from the 

 shore. One of these, the Perca scandem, is even 

 capable of climbing on the trees which grow on 

 the coast.* 



* See the account given by Lieutenant Daldorff; Linnean 

 Transactions, III. 62. I shall have occasion to notice, in the 

 VOL. I. FT 



