Sponges from South Australia. 289 



and that in ApJysina cruor tliey appear outside the cells, 

 from which tl)ej seem to have been endogenouslj derived, 

 in the form of minute granuliferous cellulas about l-2-6000ths 

 in. in diameter, still bearing the red colouring-matter of this 

 species. Moreover, in some instances, where somewhat en- 

 larged, they present a nucleus surrounded by minute granules, 

 and in this condition, losing for a time their pigmental 

 character, seem to pass gradually into the largest form of the 

 parents, the epithelial cells beside them ; hence my allusion 

 to these particulars where I have above stated that in Den- 

 drilla rosea the size of the epithelial cell " varies under 

 6-6000ths of an inch." So that, by a repetition of this pro- 

 cess, the epithelial cells and the pigmental granules are thus 

 continually renewed. 



That one function of the e]iithclial cell is to produce the 

 colouring-matter there can be no doubt ; neither can there be 

 any doubt that it does not always perform this function, for 

 in AjjJysina massa, as above stated, there is with the same 

 kind of epithelial cell no colouring-matter at all. Again, it is 

 not uncommon to find the upper and more exposed portions of 

 a sponge black (where this is the colour), while the lower and 

 more shaded ones are colourless, ex. gr. Spongia officinalis^ 

 auctt. (see ' Annals ' of 1882, vol. ix. p. 272), wherein also the 

 black colour extends for a short distance into the external 

 openings (oscules) of the large excretory canals. 



It therefore may be possible (for Nature has always 

 an unlimited number of resources) that they also possess 

 the power of the " Schleimzellen " in Mollusca, as above 

 noticed. 



In some sponges, as in Mr. Wilson's Australian one, viz. 

 Axinella atropurpnrea^ already described (' Annals,' lb85, 

 vol. xvi. p. 359), such cells, bearing the colouring-granules, 

 are dispersed generally throughout the mass, where 1 have 

 before suggested they may still be connected with the lining 

 membrane of excretory canals, although they do not present 

 the flattened form of those on the surface \ while in Suberites 

 Wilsonij the great carmine-coloured sponge of South Aus- 

 tralia brought to my notice by Mr. Bracebridge Wilson, after 

 whom I have named it, the colouring-matter appears to be 

 difluse, since I have never been able to find it in granules 

 (i. e. the cellulas of larger cells) . 



Lastly, I would observe that when the skin of an Aplysina 

 and the like sponges is stript off the surface it is found io 

 consist essentially of two layers, the outermost of which is 

 composed of epithelial cells and their pigmental granules (if 

 any) set in transparent sarcode, rendered more or less generally 



