286 Ayres' Enumeration of the 



sand, at a time when they do not choose to escape by swim- 

 ming, they fade instantly so that they show no tints but a 

 dingy white scarcely distinguishable from the sand on which 

 they lie ; if the alarm ceases, their original color returns and 

 they are again easily discernible. Many other fish possess this 

 faculty, but I have not met with any species which equalled 

 the swell-fish in the extent and rapidity of the change. 



This species, in common with the others of the genus, has 

 the power of inflating itself with air, or distending itself with 

 water. In regard to this habit, Cuvier and others have made 

 a most singular mistake. Yarrell quotes Dr. Roget in the 

 first volume of the Bridgewater Treatises as follows : '•' The 

 abdominal region being thus rendered the lightest^ the body 

 turns over, the stomach being the uppermost part, and the 

 fish floats upon its back, without having the power of directing 

 itself during this state of forced distention." How can such 

 an error have arisen ? Possibly it may have been from seeing 

 the fish only when out of the water. If after being caught, 

 and while still out of the water, it inflates itself, it then, being 

 filled with air, is of course lighter than the water, and if thrown 

 on the surface floats away with the back downward, until ex- 

 pelling the air it turns over and dives to the bottom. But 

 how different is the case when we consider the fish in its natu- 

 ral position, at the bottom, the situation contemplated in the 

 above quotation. If it then distends itself, whence is the air to 

 be derived which is to render the fish so light ? Has the fish 

 the power of mechanically separating it from the water which 

 contains it, so as to swallow the one and reject the other ? 

 The truth is, that if distended while beneath the water, they 

 are of course filled with water and not with air, so that their 

 specific gravity is neither increased nor diminished perceptibly. 

 Often, on catching them while fishing, I have held them in 

 my hand over the side of the boat so as to bring them some 

 inches beneath the surface ; and by irritating the abdomen 

 slightly with the fingers, they begin to distend themselves, and 

 soon become hard and round, as usual. If liberated in this 

 condition, they are able to swim, though more sluggishly than 



