Mr. H. J. Carter on the Polytremata. 195 



object-glass and reflected liglit in the form of delicate cobweb- 

 like extensions, stretching across them from point to point, in 

 connexion with the apertures of the Polytrema (fig.6,.s s). How 

 these delicate filaments could have survived the boisterous 

 waves of a rocky shore like that of the Mauritius it is almost 

 impossible to conceive, unless they were the dying efforts of 

 the foraminifer (whose sarcode has great vitality) after the 

 coral detritus adhering to the sponge on which it was found 

 had been finally thrown up upon the beach beyond all further 

 influence of the sea ; for such was the character of the sponge 

 which Col. Pike, U.S. Consul at the Mauritius, sent to Dr. 

 Dickie, and the latter to myself, on which I found the little 

 specimen presenting this phenomenon, which specimen is 

 now diy-mounted in a closed cell for preservation and further 

 observation. 



All this may be very clear ; but still there is Max 

 Schultze's question whether the materials above mentioned 

 got into the Polytrema " accidentally or have been taken in 

 as food." 



In the first place, it is evident that the calcareous test of 

 Polytrema requires calcareous material for its structure ; and 

 so far the calcareous element may be disposed of. But what 

 becomes of the siliceous element in the sponge-spicules ? 



Here it is necessary to remember that siliceous sponge- 

 spicules are not purely mineral and crystalline like grains 

 of quartz-sand, but are a combination of silex and organic 

 matter. Hence, if it can be shown that any organism has 

 the power of extracting this organic matter for nutriment, it 

 may be assumed that the Polytrema also may possess this 

 power. 



That siliceous sponge-spicules are destroyed by an orga- 

 nism for this purpose I have shown ('Annals,' 1873, vol. xii. 

 p. 457, pi. xvi. figs. 8 & 9) ; and that there is a cell which 

 can penetrate the walls of the spicule as Chytridium does 

 the cell-wall of Spirogyra &c. is thus proved. 



Still, as regards Polytrema^ I do not think that this can be 

 the case (certainly not with those spicules which are found im- 

 bedded in and transfixing the test generally), but that the 

 masses of spicules (which are chiefly fi'agmentary) in the caver- 

 nous cavities (fig. Q,v vv) may be inyesta^ which by accident 

 have been drawn in by the pseudopodia, and have accumulated 

 there like the hairs forming the "hair ball "of the ox's stomach, 

 or the beaks and other inyesta of Cephalopoda, which, under 

 the name of " ambergris," form a si^iilar accumulation in some 

 part of the alimentary canal of the sperm-whale. 



The presence of a sponge, too, growing over tiie surface of 



