How to obtain it. 269 
‘be held that with a low temperature they eat but little, and with a 
high one they eat greedily. There are many other influences at 
work, however, which cause them to eat more or less freely, but 
which can hardly be discussed here. It is well known that during 
the summer months they accumulate a great amount of fat, and 
thus they are better enabled to bear the starving which they get 
during the winter. 
There has been a great deal of controversy as to whether 
trout can hear. The ear of a trout may be briefly described as 
an internal organ that is tolerably well developed, and is situated 
within the cranial cavity. But it has no tympanum, nor yet any 
tympanic chamber. That a trout cannot hear in the ordinary 
way is, I think, beyond any doubt, as the ear is not constructed 
for that mode of hearing. But trout are exceedingly sensitive to 
vibration, and any sound made beneath the water, or even in the 
earth, as for instance in blasting a rock, may be transmitted by 
vibration, and the fish in this case would be immediately sensible 
that a disturbance had taken place. 
The labyrinth of the ear is well developed, but the external 
orifice is closed, and we know what is the effect on ourselves if 
we, for instance, put our fingers in our ears when anyone is 
talking. I once tried some experiments with fish with regard to 
their sense of hearing, and I.came to the conclusion that trout 
could not hear sounds made in the air, provided no agitation 
of the water occurred. The same applies to some other fishes. 
Amongst others I operated upon a shoal of herrings (C/ufea 
harengus) ina tank. Moving my hand to and fro close to the 
glass, I got the fish so accustomed to the sight that they took no 
notice of it whatever. But the moment my hand smacked against 
the glass they scattered in bewilderment. I tried shouting and 
making noises, but they apparently did not hear at all. Now, 
there is in many fishes a connection between the internal ear and 
the air bladder. In the herring, for instance, we find at the fore. 
end of the bladder two very narrow tubes or ducts, which connect 
or at least come into exceedingly close contact with the organ of 
hearing, passing right through the skull, and apparently connecting 
with the labyrinth of the ear. 
There is also in the herring a very curious connection between 
