258 J. a. WALLER ON CLTONA CELATA, ETC. 



sign, not even a fascial bundle, which in the remotest manner points 

 to an ofifensive operation, or can by any possible reasoning be 

 assumed to have had, or to have the power of " boring " or even of 

 assisting in such excavation. In some parts, the Sponge is only 

 represented by the merest film looking like a varnish, and having 

 but here and there a spicule to convince you of the organic structure 

 under your observation.* Let me call your attention to this ex- 

 ample. (PI. XXI, Fig. 3.) Here you have a portion of the lamina 

 of a shell covered with a membrane and a net-work of spicules. 

 But the membrane is the thinnest of films, which is bounded by the 

 sinuous line at base. It has scarcely a spicule upon it, until it 

 forms the net-work seen above, and the whole of this sur- 

 face is entirely destitute of any of the known excavating indica- 

 tions, until you reach that part re[)resented by shading. Tlio 

 channel on one side, however, does so, yet the membrane passes 

 over this, in no way more developed, colourless, and with scarcely a 

 spicule upon it. So here we have Sponge with no excavation, and 

 excavation with an almost invisible Si)onge.f I have noted, in my 

 previous paper, that the greatest development of the Sponge is 

 seen at the extreme edges of the shell, closing up the spaces 

 between the laminse, and at the circular orifices. In fAct, 

 it is at these orifices, that you see the most active functions 

 of the Sponge during life, most interesting to observe, when 

 the opportunity occurs, which may sometimes happen in an 

 oyster tub. Here may be found, not only the oscula, but the 

 porous system, the former often a distinct canal leading into the 

 body of the Sponge, or rather the commonwealth lining the burrows. 

 When in an active state the Sponge is protruded considerably, and 

 withdrawn again when at rest, and then the osculum is closed by 

 an array of spicules, which have their sharp points i adiating towards 

 the centre. (PI. XXI, Fig. 4.) I am indebted to Mr. Priest for a 

 specimen of this Sponge dissolved out of the shell, and it is very 

 instructive. It demonstrates completely its thin membranous char- 

 acter with spicules sparsely scattered upon it, without order, con- 

 formably to the genus Hyvieniacidon. Not a sign of any arrange- 

 ment by which the spicules could effect any erosive purpose, for 



* I am here, of course, describing the Sponge in the dried condition. 

 Bnt as I made observations on the example whilst in the fresh and Hviiig 

 state, I am enabled to mention that the quantity of sarcode follows the 

 membranous development. 



t This phenomenon is of common occurrence. 



