36 THE THREE-SPINED STICKLEBACK. 



Of the other three marine species of the genus Coitus, of 

 which more hereafter, when referring to the west coast of 

 Sweden, it may be important here to mention, that the 

 Coitus quadricornis, Linn., is a constant resident in the 

 Lake Wettern, in the central part of Sweden, a fact but 

 little . known to naturalists generally. 



The Rough-tailed, or Three-spined Stickleback (Hundstagg, 

 Stor-Spigg, Sw. ; Gasterosteus aculeatus, Linn.), was com- 

 mon in my vicinity ; as also throughout Scandinavia, from 

 the extreme south of Sweden, to far beyond the Polar 

 Circle; and this as well in the waters of the interior, as 

 on the eastern and western coasts of the peninsula. It is 

 frequently met with, indeed, in such small, isolated places, 

 that the double wonder is, in what manner it became an 

 inhabitant there, and how it can continue to exist. 



The three -spined stickleback prefers moderately rapid 

 waters, and in the summer resorts much to the shallows, 

 more especially to such as are exposed to the rays of the sun. 

 Towards autumn, on the contrary, it retires farther from the 

 shore, and in the winter retreats to the deeps ; such, at least, 

 is the presumption, for when captured at that season in 

 the fishermen's nets, it is usually in large numbers together. 

 It is seldom seen singly, but almost always in larger or 

 smaller shoals. It feeds on insects, worms, larvse, small 

 Crustacea, and the minute fry of other fish ; and although 

 of so diminutive a size, is one of the most voracious of 

 the finny tribe. 



Perhaps the most remarkable circumstance in reference 

 to this species of stickleback, is the extraordinary changes ob- 

 servable in its colours. In the winter, the upper part of the 

 head and the back is blue, and the body pure silvery-white. In 



