Page:Popular Science Monthly Volume 3.djvu/560

544 mark the difference of species. As evidence of this regularity and beauty, look at the engraving of the spicular pattern of a fossil glass-sponge (Fig. 7). Now, it should be observed of the sponges which we have given in detail, that their spicules are arranged on a six-rayed plan, or, as sometimes expressed, hexradiate. Accordingly, Prof. Oscar Schmidt has "defined the group as a family under the name Hexactinellidæ."



Many of these glass-sponges have the habit of mooring themselves by their silicious threads, and on this account are called "anchoring sponges." Though acting in this matter on one general principle, yet they have diversities of ways in carrying out this law of their nature. Hyalonema, the glass-rope sponge, plunges its long threads down into the mud, and then spreads them out like a brush. These threads have a ringed structure, so that each one has an individual hold, or