21/34 The crest acts as a tiny sail (hence the name) and communicates to the animal a slow rotatory movement while drifting before the wind. Two kinds of Janthinae (J.globosa and J.exigua) molluscs with a fragile, snail-like shell, and a vesicular float, were drifting about, and, together with a very active, silvery-blue Idotea, half an inch long, prayed upon the Velellae. At another time, among many other pelagic crustacea, we obtained three kinds of Erichthus, a genus remarkable for the glassy transparency of its species, also Hyalaea inflexa and H.tridentata, curious pteropodous molluscs which swim near the surface. Not having seen a description of this useful instrument, I may mention that the kind used by Mr.Huxley and myself, consisted of a bag of bunting (used for flags) two feet deep, the mouth of which is sewn round a wooden hoop fourteen inches in diameter; three pieces of cord, a foot and a half long, are secured to the hoop at equal intervals and have their ends tied together. When in use the net is towed astern, clear of the ship's wake, by a stout cord secured to one of the quarter-boats or held in the hand. |