BRITISH FRESH-WATER FISHES
produce sufficient eggs to satisfy his desires. After the first batch are laid, a second female is invited to add to the number, and this operation is repeated by others several times. If the nest is damaged the male will undertake the necessary repairs, and he will aerate the water by quick movements of his fins. The materials composing the nest are fastened together by a sticky substance with which this species is provided.
It should be mentioned that rough-tailed and smooth-tailed forms of Three-Spined Sticklebacks occur in Britain, but the latter are mostlv found in inland waters, and there are also intermediate forms. These, however, need not detain us.
Ten-Spined Stickleback.—Pygosteuspungitius (Fig. 59). I'his well-distributed species is at once distinguished by the larger number of short sharp spines along the back. Although called Ten-Spined, the back spines may consist
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of from 7 to 12, and there are others below as in the species last under review. This is smaller than Gastrosteus aculeatiis, rarely exceeding 3 inches in length. In its general life-history this species closely resembles its lesser-spined cousin, but it is more of a fresh-water inhabitant. It is dark greenish, dotted with black.
