Most of them have tentacles on the head by which they assist their movements among the rocks and stones; and some actually creep up the rugged surfaces of rocks by means of their ventral fins. They can all live for a long time out of the water, being able to retain a supply of water in their expanded gill-chambers to keep the gills moist. [Illustration: FIG. 239.--THE SMOOTH BLENNY] The Smooth Blenny or Shanny (_Blennius pholis_) is one of the commonest species. It reaches a length of four or five inches, and has no tentacles on the head. The Eyed Blenny or Butterfly Blenny (_B. ocellatus_) may be distinguished by the conspicuous spot on the spinous portion of the dorsal fin. The Large Blenny (_B. gattorugine_) inhabits deeper water, chiefly off the south-west coast, and reaches a length of a foot or more. The Crested Blenny (_B. cristatus_) is named from the small crest on the head which can be raised and depressed; and the Viviparous Blenny (_Zoarces viviparus_), as its name implies, brings forth its young alive. The last species often exceeds a foot in length, and is found principally on the north and east coasts. The newly-born young are so transparent that the circulation of the blood within the body may be seen under the microscope quite as easily as in the web of the frog’s foot and in the tail of the tadpole. One very common species of the _Blenniidæ_ differs considerably in general form from the others, its body being elongated and eel-like, but much compressed laterally. We refer to the Butterfish or Butter Gunnel (_Blennius gunellus_), which is often mistaken for a small eel by young sea-side naturalists. It is exceedingly common under stones at low tide, and may be recognised at once by the light rectangular spots along the flattened sides of the body. It is quite as slippery and as difficult to hold as the eel itself. It will be interesting to note that the ugly Sea Cat or Wolf-fish (_Anarrhichas lupus_), which is sometimes sold for food in our large towns, is also a member of the blenny family. It is a powerful, rapacious fish--a veritable wolf of the sea, always ready to attack anything. It feeds on molluscs and crustaceans, the shells of which are easily reduced between the powerful crushing teeth that line the jaws behind the formidable canines. [Illustration: FIG. 240.--THE BUTTERFISH]