52 On a new Species of ' Echinonematous Sponge. 



though presenting a strangely organic appearance, is yet able 

 to resist the effects of boiling solution of alkali ? From the 

 fact that some small pieces of cork, which were accidentally 

 present with the boiling spicules, had not suffered any marked 

 decomposition, nothing more than a separation, to a certain 

 extent, of their cells, it occurred to me that it might be a form 

 of cellulose, which is known to occur now in various groups 

 of animals, and which would not be an unlikely accompani- 

 ment to the green colouring-matter (probably chlorophyll) 

 which characterizes some kinds of sponges. On testing with 

 Schulze's solution, however, the membrane was not coloured, 

 while the associated fragments of cork became stained of a deep 

 violet ; on exposing to a high temperature it appeared to 

 become carbonized ; it did not affect polarized light. These 

 are the only observations I have made with regard to this 

 substance at present ; my next step will be to submit some 

 sponge-spicules to organic analysis ; till then I regard the 

 composition of their organic foundation as an open question. 



The heads of the axial spicules appear to suffer far more 

 from solution than their shafts, the whole interior of a head 

 being sometimes eaten out without the shaft showing any 

 evident signs of solution. Can this in any way be connected 

 witli the micro-tuberculation of the heads ? 



Fig. 4. 



Two of the double-headed axial spicules after boiling with potash 

 (X 435). Shaded parts indicate the cavities which have been 

 excavated by solution. 



From the cavity thus excavated in the head, the potash 

 sometimes finds its way into the axial canal; but quite as 

 often it dissolves a path for itself outside the site of the axial 

 canal down each side of the spicule. 



EXPLANATION OF THE PLATES. 



Plate VI. 



Plocamia plena. 



Fig. 1. Plocamia plena (nat. size), b, incrusting base; s, single upright 

 stem ; r, a rib of the fan-like expansion cut across (the fan is 



