CHAPTER II 
THE BREATHING APPARATUS OF FISH, THEIR 
TEETH, AND ORGANS OF SENSE 
The Gills—The Teeth—The Sense of Touch—The Sense of Sight—The Sense 
of Hearing—The Sense of Smell. 
An attempt to deal with the internal anatomy of fishes 
would be not only beyond the scope of the present work, 
which aims no higher than to give a popularly intelligible 
description of the fishes found in British lakes and rivers, but 
would also exceed the powers of the author. Nevertheless, 
any review of these creatures which is more than purely 
superficial must take account of the manner in which their 
existence has been affected by residence in the water, and the 
degree in which their principal organs have been modified in 
conformity with their environment. 
The breathing apparatus of fish is of peculiar interest, 
owing to the density of the medium from which it is its 
office to extract dissolved oxygen. The water 
which enters the mouth passes through a cavity 
containing the gills or branchie, which consist of a series of 
cartilaginous rods, borne upon the convex or posterior face 
of the branchial arches (Fig. III., 58, 61), and flattened and 
tapered towards the free end. These are the branchial /amelle, 
each of which is enclosed in a mucous membrane containing 
also the capillary blood-vessels. It is these capillaries which 
give the gills their brilliant red colour ; they are fed by an 
artery which sends a branch into every pair of /amelle, which 
22 
The gills. 
