ATTITUDES EXPRESSING EMOTION 7 
for more than a second or two in this attitude of alarm, 
and it was only because this perch was particularly 
tame that he had the pluck to resent the tapping on the 
glass. A wild fish would have rushed off, knocked its 
head against the end of the tank, and then sulked on 
the bottom. 
Most fish show their alarm by erecting their fins, 
but a few, in addition, strike attitudes peculiar to 
themselves. The cottus puffs out his cheeks; the 
blenny frequently, though not invariably, curls his 
tail towards his head ; the carp bends the end of the rays 
of the tail fin at right angles; and in all probability 
observation will show that most fish have some char- 
acteristic way of showing their alarm. 
I have illustrated how a fish becomes pale with fear 
but some tropical fishes actually change their colour. 
This is due to the fact that fear makes the colour cells 
in the skin contract, and the colour of the skin with 
contracted cells is different from the same with relaxed 
cells. 
In order to obtain photographic illustrations of the 
attitudes and movements of fishes, it is necessary to 
give a rapid exposure, usually one-hundredth of a 
second. This is only possible when fish are photographed 
in a glass tank, with a good light, but a wild fish with 
this unusual illumination is too alarmed to be natural. 
It is only after a fish is sufficiently accustomed to the 
light to feed freely that photographs of attitudes are of 
any value. It would be quite reasonable to question 
