FISHES AND SEA-SQUIRTS. 311 



to life in fresh water and others to life in the sea, the 

 capacity for change prevents the fixation of these varieties 

 as new species. 



Of the large cod family we have already described one 

 member, and cannot devote more space to it or the related 

 haddock, whiting, cod, pollack, etc., most of which, as strong 

 swimmers, are more or less outside our range, though many 

 of them may be caught off the margin of the rocks. 

 Leaving them we may pass on to the sand-launces, or sand- 

 eels, which may be found in immense numbers near the 

 mouths of tidal rivers, in shallow water over a sandy bottom, 

 or by digging in the sand. Beautiful silvery creatures they 

 are, darting like shadows through the water, or burying 

 themselves with swift movements in the sand. Like the 

 young saithe, which swim in similar shoals, they are eagerly 

 attacked by sea-gulls, as well as by predaceous fish and 

 porpoises. On the calm summer days when the water is 

 so still that thistle-down, blown from the neighbouring 

 dunes, floats on its surface, and so clear that the bottom 

 seems within the reach of the hand, on such days one 

 often sees flocks of screaming sea-gulls circling over dis- 

 coloured patches in the water, and ever and again darting 

 downwards to emerge with a silvery fish from the dense 

 shoals in the water. In the same way the gulls collect 

 about the river mouth as the tide ebbs, and seize the little 

 fish as they swim in the shallows. That this fate may not 

 overtake all, nature has furnished them with a protruding 

 lower jaw, which forms an efficient shovel, by means of 

 which the little fish may bury themselves deeply in the 

 sand. In some places the sand-eels are caught in large 

 numbers for bait and food by raking with hooks or rakes 

 the loose sand in which they live ; sometimes they are 

 merely dug for like sand-worms, but, as all boys know, they 

 may also be caught in a fine shrimping-net, or even by hook 

 and line. 



There are two common sand-eels, the greater (Ammodytes 

 lanceolatus) and the lesser (A. tobianus, see Fig. 2), the 

 latter being perhaps the commoner of the two. A little 

 care is required to distinguish the two at first, but once 

 the differences have been accurately noted the task becomes 

 easy. As to size, the lesser sand-eel is usually only three 



