192 ARTHUR DENDY. 



In this genus we always find, at the end of each radial 

 chamber, a more or less dense tuft of oxeote spicules (figs. 2, 

 3, 6 — 8). The shape of these spicules varies greatly, and 

 influences in a remarkable degree the character of the surface 

 of the sponge. They may be enormously elongated and pro- 

 ject far beyond the surface, which thus becomes covered with 

 a coating of long silky hair, as in SyconRamsayi; or their 

 outer ends may be swollen and nail-shaped and project but 

 very slightly, so as to form a dense crust, as in some specimens 

 of Sycon gelatinosum (fig.6). All conditions intermediate 

 between these two may also be met with. These tufts of uni- 

 axial spicules, which are extremely characteristic of the genus 

 Sycon, doubtless serve to protect the surface of the sponge 

 generally, and also to filter the water before it passes into the 

 '' inter-canals." The entrances to the " inter-canals,^' between 

 the tufts of oxeotes, may also be protected by the basal rays 

 of the more distal tubar triradiates, which may curve outwards 

 from the chamber wall, as in Sycon ensiferum (4). 



In Sycon boomerang, as I have already had occasion to 

 point out, we meet with the first indication of a true dermal 

 skeleton distinct from that of the chambers. It consists of a 

 few scattered triradiate and oxeote spicules lying in the thin, 

 pore-bearing membrane, which stretches across and protects 

 the entrances to the intercanals (fig. 8) . 



In this genus we frequently meet with a more or less specially 

 developed "oscular skeleton," which when present, either in 

 this or any other geuus, always consists of a fringe of oxeote 

 spicules, projecting more or less markedly around the osculum. 

 Usually the fringe is vertical, or inclined only at a slight angle 

 to the long axis of the gastral cavity ; but occasionally a second, 

 almost horizontal, fringe is developed, which projects almost 

 at right angles all around the base of the first one. A beau- 

 tiful illustration of such a horizontal fringe is given by 

 Haeckel in the case of his Sycarium elegans (5, pi. Iviii), 

 and I have also met with it in a variety of Sycon gela- 

 tinosum from Port Jackson. The oscular skeleton is, 

 however, a very variable structure, and of very little import- 



