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 mostly found in inland waters, 
and there are also intermediate forms. These, however, 
need not detain us. 
Ten-Spined Stickleback. — Pygosteus pungitius (Fig. 59). 
This 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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SSL TTT tee 7 7 
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Ten -spined Stickleback Fig 59. 
of from 7 to 12, and there are others below as in the 
species Jast under review. This is smaller than Gastro- 
steus aculeatus, 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. 
106 
