42 Mr. W. J. Sollas on the 



Trichite sheaves are common in a variety of sponges, espe- 

 cially among the Esperiadaj. Oscar Schmidt * has described 

 the structure of those which occur in Esperia lucifera, Sdt. ; 

 he, however, represents the nucleus as occurring at the side of 

 the sheaf, and not at the end, as shown in my drawings. 

 The enclosing cell-membrane is also more distinct in his 

 figures than I have yet seen it. Possibly his specimens 

 represent an earlier stage in the history of the sheaf than 

 mine, and the nucleus may subsequently become trans- 

 ferred from the side to the end of the cell. In Schmidt's 

 fig. 21, which represents a mature cell, this, however, does 

 not appear to be the case, and we must probably fall back 

 on inherent differences in the spicule-sheavcs of the two 

 sponges. 



4. Foreign Particles. — The congregation of foreign parti- 

 cles on the exterior of the sponge, and their abundant distri- 

 bution within it, are very striking facts, though not by any 

 means confined to this species or genus; as one observes the 

 numerous remains of organisms imbedded in the sarcode of 

 the mark one can scarcely retrain from regarding them, like 

 the wings of flies in a spider's web, as the remnants of pre- 

 vious feasts. The cortex is so admirably adapted for pre- 

 venting the entrance of foreign bodies, especially of the size 

 of those under consideration, that it is difficult in the extreme 

 to see how those within the mark can have found their way 

 there unless through the cooperation of the sponge itself. If 

 this theoretical view be the true one, then we may further 

 regard the forked ends of the projecting spicules as serving 

 not only for a means of defence, but as actual traps for cap- 

 turing prey and so securing a constant supply of highly pro- 

 teinaceous food for the sponge. 



5. Classification. — Of all the various species of the genus, 

 Stclletta Normani is provided with the most complete equip- 

 ment of spicules ; and no difficulty is likely to be encountered 

 in its identification. 



The following list of the already published species of Stel- 

 letta may prove useful for reference. I have not included 

 in it those species of Bowerbank's Ecionema and Teihija 

 which may probably turn out to be Stelletta, because I 

 think this genus cannot last much longer without under- 

 going modification, and I am anxious not to transfer Bower- 

 bank's species to it till both it and they have been subjected 

 to revision. 



* Zoologische Ergebnisse der Xordenfahrt voni 21. Juli bis 9. Sep- 

 tember 1872, p. 120, pi. i. figs. 19-21. 



