278 



UTILITARIAN ZOOLOGY 



importance to Russia. The flesh of all the species is used as 

 food, the hard roes (ovaries) are cleaned and salted to figure as 

 caviare, to the extent of some 10,000 tons annually, and isinglass 

 is prepared from the swim-bladders. For all these purposes 

 the smaller sorts of Sturgeon, especially the Sterlet, are most 

 esteemed. The Volga fishery is on the largest scale, and goes 

 on at two seasons, autumn and winter. During the former, 

 ground-lines with numerous hooks are used, and operations cease 



when the river begins to freeze. 

 With increasing cold the fishes 

 congregate at certain spots for 

 hibernation, and such places 

 are carefully marked by the 

 fishermen. Later on, in Janu- 

 ary, when the coki is at its 

 maximum, the winter - fishing 

 is ushered in with g-reat fes- 

 -PEcf-oRALFini tivities. Good-sized holes 

 are broken through the ice 

 at the spots previously noted ; 

 the fishes, disturbed by the 

 noise, come to the surface, and 

 are promptly secured by means 

 of harpoons and iron hooks. 



Skates and Rays (Bat- 

 oiDEi). — These flattened, nar- 

 row - tailed, rhomboidal forms 

 constitute, with Sharks, Dog- 

 fishes, &c., the great group of 

 cartilaginous fishes (Elasmobranchii). The two most important 

 British species are the comparatively smooth - skinned Skate 

 {Raia batis) and the Thornback (/?. clavata, fig. 1205), of which 

 latter the characters are sufficiently indicated by the name. The 

 Skate may attain a length of 6 feet or more, and the Thorn- 

 back about half as much. Both are common in British waters, 

 where they are captured by trawling and by line-fishing. Though 

 not among the choicer food-fishes, they are largely eaten, the 

 enormous pectoral fins, cut into strips and rolled, constituting what 

 is commonly known as "crimped skate". 



Round Mouths (Cyclostomata). — The eel -shaped scaleless 



CAUDAL FIN 



DORSAL FlN3"^ 

 Fig. 1205.— Thornback {Raia clavata) 



