24 BRITISH FRESH-WATER FISHES 



slight lesion of the branchi^ ; 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 (^Ibid., 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 [Ibid.^ 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 — external 

 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 



* 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. 



