288 Mr. H. J. Carter on 



of the larger oscules " (l, c. p. 4) ; also that the same kind of 

 cells are arranged " on the surface " of Stelletta aspera " in 

 a tessellated manner " in " distinct cavities " of the same kind 

 of sarcodal trama or tibrillous structure as in Dercitus niger^ 

 while Piiou cells were not only to be found on the surface, 

 but also " scattered throughout the sponge generally " (pro- 

 bably in connexion with the epithelial lining of the excretory 

 canals), together with here and there a cell charged with 

 black granules, also precisely like those of Dercitus niger 

 {lb. p. 7). Thus it was observed that the material of the dark 

 pigment was seated in the " granules " themselves, that is 

 little cellular, although not always making itself visible. 



Unfortunately a typographical error occurs here which 

 causes the measurement of these cells to appear as " 1-1 70th 

 of an inch " in diameter, instead of l-750th or 8-6000fhs, 

 which it ought to have been ; thus they are a little larger than 

 those of Dendrilla rosea, which, according to my measuring, 

 vary under 6-6000ths, as will more particularly appear here- 

 after. 



Schulze alludes to a layer of these cells in Aplysina cero- 

 plioha under the term '" ectoderm " (Zeitschrii't f. wiss. Zoo- 

 logie, Bd. XXX. p. 392), and Lendenfeld docs the same under 

 the name of " Plattenepithel " in Dendrilla rosea {ib. Bd. 

 xxxviii. p. 281, Taf. xii. fig. 19 Ec), while Pole] aefi' has 

 given a representation of them in his Cacospongia vesicuiiferay 

 adding that they are " not dissimilar to the renowned and 

 still debatable ' Schleimzellen ' of Mollusca, as Dr. Fleming 

 has drawn them, and thoroughly identical with the vesicular 

 cells of many Desmacidonidaj undescribed hitherto, but 

 undoubtedly very well known to every spongologist who has 

 had to deal with the representatives of the family [Spongelidaj] 

 just mentioned " (' Challenger ' Reports, 1S84, Keratozoa, 

 p. 59 of separate copy). 



In some fragments of the soft, tibro-reticulated, dermal 

 structure of a specimen of Dendrilla rosea which had fallen 

 off from the skeleton during maceration, the circular cavities 

 alone occupied by some of these cells remained, even after 

 portions had been stained, dried, and mounted in balsam, so 

 that it became perfectly evident that they had been imbedded 

 in the fibre of the fibro-reticulated structure of the surface in 

 distinct compartments similarly to those above mentioned 

 which exist in a similar tissue in Dercitus niger • so that these 

 epithelial cells do not always appear to be confined to a simple 

 lamina. 



I have already stated that their granules in Dercitus 

 niger bear the black-brown colouring- matter of this sponge, 



