22 SCIENCE SKETCHES. 



tion in this Centennial year, for he is altogether an 

 American product. He has all that ardent desire 

 for perfect freedom that is supposed to be native 

 to this continent. Unless all appearance of cap- 

 tivity be concealed in a well-kept aquarium, he 

 will quickly lie on the bottom, dead. Here, at 

 the beginning (for much as we may regret the 

 fact, the death of some individual must precede 

 our acquaintance with the group, and even to some 

 extent with the individual himself), we observe 

 two noteworthy facts : the fish in dying does not 

 turn over, and does not rise to the surface. On 

 dissection, we find that the air-bladder is only 

 rudimentary, being structurally, but not function- 

 ally, present, a distinction not without meaning 

 in these days of evolutionary hypotheses. If our 

 tank be so arranged that the conditions are nearly 

 natural, there being an abundance of stones and 

 weeds on the bottom, our Johnnies will cheerfully 

 live with us, and we shall be ready to study their 

 individual peculiarities, or, as Boyesen's "Scientific 

 Vagabond " would have said, their " psychology." 

 For it must be known that while all fish are fish, 

 they are so only as all men are men. The chil- 

 dren of one family are not more unlike one another 

 than the fishes of one brood might be if the sickly 

 ones and the lazy ones were as carefully guarded 

 as are ours. As it is, they have their individuality. 

 One is constantly darting over and among the 

 stones, never resting, moving his head from side 

 to side when his body is for a moment still. An- 

 other will lie for hours motionless under a stone, 

 moving only for a fe.w inches when pushed out 



