278 THE AMERICAN NATURALIST. [VoL. XXXIV. 
the water are not perceived or are ignored, and apparently 
stationary objects are not perceived when the fish approaches 
them. Ifa rod is held in the hand, the fish always perceives it 
when within about half an inch of it, and backs water with its 
pectorals. If the head of a fish is approached with a rod, the 
direction from whence it comes is always perceived and the 
correct motion made to avoid it. This reaction is much more 
intense in the more active young than in the adult. One 
young about 10 mm. long determined with as great precision 
the direction from which a needle was coming as any fish with 
perfect eyes could possibly have done. It reacted properly to 
avoid the needle, and this without getting excited about it.” 
That fishes with perfect eyes depend entirely upon them in 
the detection and capture of their prey is easily proved by the 
difference in their behavior when feeding in perfectly clear or 
in muddy water. This experiment can be made ina large 
aquarium containing a number of hungry black bass, and turn- 
ing a few small yellow perch loose among them. If the water 
be clear, short work is made of the victims, but their capture is 
made less and less certain the muddier the water happens to 
be. It is more than likely that some of the semi-blind deep- 
sea fishes, as, for example, Mancalias shufeldtit, are quite as 
sensitive to disturbances of a very delicate nature of the water 
in their immediate neighborhood as is Amblyopsis of the Mam- 
moth Cave of Kentucky. Onthe other hand, the eyes of some 
of these fishes have come to be of enormous size in proportion 
to the size of their owners, and this to gain all the available 
light possible. Consequently, there is probably a compensat- 
ing distinction in this regard among such fish as I have here 
noticed; in other words, the more perfect the sight the less 
need of a highly organized sensitive apparatus and vice versa. 
But now comes another question in the behavior and psy- 
chology of fishes that will require a far greater knowledge on 
our part of the habits and history of these vertebrates, before 
biologists will arrive at anything like a unanimity of opinion 
regarding the matter, or the observations in the premises, and 
the observed facts are sufficiently numerous to insure the solu- 
tion of the entire problem. It involves the whole question of 
