544 THE POPULAR SCIENCE MONTHLY. 



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 spicides are arranged on a six-rayed 

 plan, or, as sometimes expressed, hexradiate. Accordingly, Prof. 

 Oscar Schmidt has " denned the group as a family under the name 

 Hexactinellklce." 



Fig. 9. 



Ventricttlites Simplex. A fossil sponge, once and a half the natural size, showing the surface 

 ornamented by a regular arrangement of ventricles. (See Pig. 10.) 



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. 

 JZyalonema, 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 



