24 BRITISH FRESH-WATER FISHES 
slight lesion of the dranchie ; wherefore, to close the gill- 
opening more effectively, its margin is further protected by a 
membrane supported upon one, two, or several bony rays, 
distinguished as the branchiostegals (Jéid., 43).* As a pro- 
tection from internal injury, such as might be caused by hard 
substances carried into the mouth by the water, the branchial 
rays, which carry the gills on their posterior face, are armed 
on their concave or anterior surface with a number of horny 
processes called gill-rakers (did., 63). 
The usual number of gills in Teleostean fish is four pairs. 
The sturgeon, a Ganoid fish, has one additional imperfect gill in 
front of the others, and also what are called spiracles—externai 
openings on the head to a canal leading into the pharynx, and 
connected with the respiratory system ; but it is destitute of 
branchiostegal rays. 
The gill-opening, usually large and conspicuous in Teleostean 
fish, is very small in the eel ; and in the sub-class Cyclostomata 
(lampreys) it is replaced by seven small circular apertures on 
each side of the head behind the eye. 
Most Teleostean fish swallow their food whole; and as the 
great majority of British fresh-water fish are carnivorous, cap- 
turing their prey by pursuit, it is upon their teeth 
only that they have to rely, having no talons or claws 
like predaceous mammals, birds, or reptiles to assist them. The 
teeth of these fish, therefore, are pointed and prehensile, un- 
suitable for cutting or bruising withal. But our list includes 
many fish of the Carp Family which are partly herbivorous, 
browsing on the foliage of water plants and submerged grasses. 
The mouth in these fish is toothless, but they carry in their 
The teeth. 
* Often have I had occasion in spring fishing for salmon to remonstrate 
with my gillie, who, in unhooking a kelt in order to return it to the water, 
is apt to thrust his fingers rudely under the gill-covers as the most con- 
venient way of holding a slippery customer. Such treatment usually 
causes the death of the fish, which it is the angler’s duty to return to 
the river unhurt. 
