Page:Popular Science Monthly Volume 66.djvu/573

Rh is a greater wealth and variety of life than can he found in an equal area elsewhere in all the Bermuda archipelago. Located on the very edge of the outer reef, where breakers are always running, save in perfectly calm weather, the conditions seem to be especially favorable for many of the marine organisms. Numerous small and brilliantly colored fishes dart about in the pools, and escape into the crevices of the rock as one attempts to scoop them up. The great black sea-urchin (Diadema setosum) bristling with slender spines is firmly ensconced in niches in the rocky floor and usually defies all attempts at removal. But by breaking away the rim of protecting rock this urchin may sometimes be dislodged. Unless great care is used, however, his spines, which are like needles, will penetrate the flesh, where they are sure to break off and become a source of great irritation if not promptly removed; but they are so brittle that removal is not an easy matter. Crabs both great and small are everywhere, and the little hermits with their molluscan shelters of various kinds and sizes make a grotesque appearance as they scuttle away to cover.

One of the most novel sights that I saw in these tropical seas was viewed through a water-glass near North Rocks. A school of small fishes (Atherina) swimming in a nearly spherical mass ten or fifteen feet in diameter, seemed to be slowly revolving through the water as its individuals swam round and round in an almost solid mass. It was not at first apparent how the mass preserved such a constant form, but at length it was seen that a few individuals of another and larger species of fish were acting the part of the shepherd dog, and that the smaller fishes were actually being herded—a flock of submarine sheep. Nor do the herding fishes prey upon their flocks. The explanation is interesting. Three kinds of fishes are involved in this association. The herders accompany and ‘round up’ the smaller fishes, so that other kinds of fish which are wont to prey upon them may, as they approach with murderous intent, fall victims to the herders.

Picturesque Castle Island, which still contains ruins of early fortifications,—some of them possibly dating from the early part of the seventeenth century,—once guarded the entrance from the sea through the channel of Castle Roads. From the floor of this channel the dredge brings up many interesting animals: the great conchs (Strombus gigas), the shells of which are still prized by tourists, living Foraminifera of several kinds, and, best of all, the Caribbean Amphioxus. This species was dredged in considerable numbers at various places during the summer of 1903, and especial attention was given during the past summer to finding out how widely it is distributed, and the conditions under which it thrives. As a result