HEARING AND ALLIED SENSES IN FISHES. 
61 
Having reached the conclusion that the downward swimming of the fishes could 
be brought about by stimulating the lateral-line organs through slight mass-move- 
ments of the water, I next attempted to ascertain the relative importance of different 
parts of the lateral-line system in this reaction. I prepared one set of the fishes in 
which the lateral-line nerves were cut close to the pectoral girdles, thus rendering 
ineffective the lateral-line organs of the trunk while those of the head were left 
intact. These individuals responded in all respects, so far as I could see, as normal 
fishes did, and I therefore concluded that the lateral line proper was not an essential 
part of this system of sense organs. 
In the second set of fishes I cut the fifth and seventh nerves of both sides, thus 
preventing the lateral-line organs of the head from acting. These animals always 
descended when the aquarium was shaken, but with noticeably less precision than in 
the cases of normal individuals. It therefore seemed probable to me that the por- 
tion of the lateral-line system on the head was more effective than that on the trunk, 
but as this experiment involved cutting the general cutaneous nerves of the head 
as well as the lateral-line nerves, the experiment is not wholly conclusive. 
Finally, in a third set of fishes, I cut the lateral-line nerves and the fifth and 
seventh nerves of the right sides only, leaving the left sides intact. These fishes, 
though a little sluggish, reacted in an essentially normal way. From these three sets 
of experiments I conclude that the lateral-line organs maybe considerably reduced 
without seriously impairing the action of the system as a whole, though the portion 
of the system on the head is less easily dispensed with than that on the trunk. 
The shin in Fundulus heteroclitus . — While I was experimenting on fishes in 
which the lateral-line organs had been rendered inoperative I was at times puzzled 
by getting reactions that seemed contradictory to the general conclusion that such 
fishes were not stimulated by a slight movement of the whole mass of water. Occa- 
sionally on making the whole aquarium move slightly a fish without lateral-line 
organs would swim rapidly to the bottom. On watching for instances of this kind 
I soon found that they occurred only when the fishes were close to the top of the 
water, and in fact were within the range of wave action. When the whole aquarium 
was moved, even only slightly, the upper surface of the water was thrown into small 
waves. These waves, as could be seen by the motion of small suspended particles, 
extended only a few centimeters below the surface of the water, but they established 
a region into which the fishes without lateral-line organs would not ascend, and 
from which, if overtaken by the waves there, they immediately escaped by swimming 
downward. As fishes without ears as well as without lateral-line organs were stimu- 
lated by these surface waves, I concluded that in this instance the motion of the 
water must affect the general cutaneous nerves (touch). 
If the motion of surface waves is a stimulus for the general cutaneous nerves, 
it would seem probable that currents in the water would also affect these nerves and 
that the ability of a fish to head up a stream might depend rather on the stimula- 
tion of its skin than, as Schulze has implied, on the stimulation of its lateral-line 
organs. Fundulus is in a marked degree rheotactic, i. e., it swims vigorously against 
a current, and I therefore resolved to test this fish to ascertain whether its rheotaxis 
depended on its lateral-line organs or not. Six specimens, in which the nerves to 
the lateral-line organs had been cut, were placed one after another at the open end 
of a large glass tube through which a moderately strong current of sea water was 
flowing. All swam energetically up the tube, and, so far as this reaction was 
