40 JOURNAL OF THE [February, 



that one wheel of the bobbin is inside of the shell, like the rivet- 

 head in a boiler, and the other wheel is outside of the shell, and 

 projects a little in order to be entangled in the felting of the 

 skeleton spicules of the body mass of the sponge. I have liken- 

 ed these little spicules on the statoblast to a bobbin, or spool. 

 Their technical name, though in English, is somewhat formid- 

 able, since they are known as the " short birotulate statosphere 

 spicules." 



5. This brings us to another point of interest. Interspersed 

 somewhat sparingly among these short birotulate spicules, which 

 are practically innumerable, is another double-headed spicule, of 

 about twice the length of those just described, and differing 

 from them greatly in the character of the two ends. Technically 

 it is termed birotulate. This word, however, is not so accurately 

 descriptive of these, as it is of the bobbin-shaped spicules. These 

 long statosphere spicules deserve to be called double-grapnels ; 

 for each end is, not a wheel, but a series or circle of hooks. In 

 this way extraordinary holding power is afforded, to secure the 

 statoblast during its winter stay in the skeleton of the colony. 



Generally the shaft, or axle, of the short bobbin-like spicule is 

 smooth, though it is sometimes a little spurred. But in the 

 larger, or grapnel spicule, the spurring of the shaft is so frequent 

 and so pronounced, as to excite curiosity regarding its function. 

 I hardly dare attempt an interpretation, farther than to suggest 

 that this arrangement gives to the shaft a steadier hold in the 

 shell of the statosphere. 



