The allied species include the very small Two-spotted Sucker (_L. bimaculatus_), which is of a bright red colour, and adheres to stones and shells in deep water; the Sea Snail (_Cyclopterus liparis_), about four or five inches long, with a soft and slimy semi-transparent body; and Montagu’s sucker (_C. Montagui_), which is usually under three inches in length, and may be distinguished by its peculiar habit of curling the body laterally when at rest. Equally interesting are the little Sticklebacks (family _Gastrosteidæ_), the fresh-water representatives of which are known to almost everyone. Their pugnacious habits, the bright colours assumed during the breeding season, and the wonderful nests which they build for the protection of their eggs and young, have all served to make them popular with those who take interest in the forms and ways of animals. They are, moreover, such hardy creatures that they may be kept alive for a considerable time in any well-managed aquarium. [Illustration: FIG. 238.--THE FIFTEEN-SPINED STICKLEBACK AND NEST] In this family the hindmost portion of the dorsal fin is soft-rayed, but the front portion is represented by a row of strong, sharp, erectile spines, which constitute a formidable weapon of offence and defence. Most of the species live in fresh water, but all the members of the family seem to be able to live almost equally well in both salt and fresh water. We have one marine species--the Sea Stickleback or Fifteen-spined Stickleback (_Gastrosteus spinachia_), which may be caught on rocky and weedy coasts. It derives one of its popular names from the presence of fifteen spines along the middle of the back. Its tail is long and narrow, and its snout elongated, with the under jaw projecting beyond the upper. The nest of this species is a pear-shaped mass of soft sea weeds and corallines, all bound together by a silky secretion, and suspended to the rock in a sheltered spot. Within this the female deposits her eggs in little clusters, all of which are bound together and to the nest itself by the silk. If the nest is damaged while occupied, it is immediately repaired, the male, it is said, taking upon himself the responsibility of this task.