gular fanning with its filmy pectoral fins. This habit seemed to me at first useless and unaccountable, but on consideration I have little doubt that its purpose is to produce a more free and rapid change of the surrounding water; and that it is one of those compensatory actions that we frequently meet with in physiology, and that are so interesting.
In the tropical seas I have had many occasions of witnessing the actions of a still more singular Sucking-fish, the Echeneïs. The notion put forth in books, that this fish, being a very slow swimmer, needs to be carried along by others, is simply absurb, and must have been formed by those who never saw the fish alive. It is in no wise inferior, in swiftness or power, to fishes of the same size with which it associates, the Sharks for instance to which it so commonly affixes itself. The Echeneïs bears a very close resemblance, when seen in the water, to a young Shark. It is fond of attaching itself to a grown Shark, usually choosing a spot just behind the pectoral fin, but it as commonly adheres to the rudder or to the bottom of a ship. I have thought that the singular habit may be connected with its manner of taking food; especially as the mouth, owing to the projection of the lower jaw, opens on the upper side of the muzzle. Now when the coronal disk is affixed to any foreign body, the lips are made to touch the latter also. We know that there are multitudes of minute animals, such as Crustacea, Cirripedia, &c. that live parasitically on the bodies of marine animals, and on foreign objects habitually submerged. If the Echeneïs feeds on these, there is
