the sponge, but almost always lining the cavities or hollow 

 passages of the mass. They are likeAvise to be found as a 

 lining all over the surface of the sponge, but in no place are 

 they to be met with arranged in so regular a fashion as on 

 the meshes of the network covering the oscula. From the 

 peculiar way in which they are placed on the edges of the 

 meshes, and from the fact that the barbs on the stem of the 

 spicules all point in the one direction, it is possible that 

 while it would be easy to glide over the slimy sarcode down 

 into an osculum, return would be no easy task, as any solid 

 body would be at once caught and retained by the barbs. 

 From the manner in which the cruciform basal portion of 

 these spicules is inserted in or attached to the sarcode, I 

 make no doubt but that they are subject to being moved up 

 and down and to and fro, and that on the contraction of an 

 osculum, and on the consequent discharge of water from the 

 oscular cavity, the spicules are pushed outwards and upwards, 

 falling down again on the expansion of the osculum. In all 

 the numerous writings on the structure of Hyalonema, I 

 cannot find that the exact position of these spicules in the 

 living sponge has been determined. I have, therefore, 

 tliouglit it advisable to give the accompanying illustration 

 (Plate III), for which I am indebted to Mr. Lens Aldous. It 

 represents one of the oscula removed from a specimen of H. 

 mirabUis in the Lisbon Museum. The spiculate cruciform 

 spicules which line the edges of the sarcode network are very 

 easily displaced, and but comparatively few of them were 

 on the specimen drawn by Mr. Aldous, but in a living state 

 they line, packed in a close row, the edges of the sarcode 

 mesh; they diifer slightly from any of those figured by Dr. 

 Bowerbank or Max Schultze. One other subject I should like 

 here to allude to. The oscula of H. mirabilis being now dis- 

 covered and described, and they being found to be just those 

 that one Avould have expected and just in the position in which 

 one would have looked for them, it scarcely requires my state- 

 ment that I saw the little parasitic Polythoa in a living state 

 on the siliceous axis of the Hyalonema, and that I watched 

 them expand their tentacles, after the fashion of any other zoan- 

 tharian, to prove that though they have mouths these mouths 

 arc their own, and not at the service directly or indirectly 

 of the Hyalonema. Is it too much to expect to settle the 

 last lingering doubt that may still exist in some minds as to 

 the nature of these independent though parasitic organisms? 



^. Aphrocallistes Bocagei, sp.nov. (Plate I.) 

 Sponge fistulous, erect, branching somewhat irregularly ; 



