522 ARTHUR DENDY. 



By far the larger and most important portion of the skeleton 

 lies within the ectosome. It may be best studied by cutting 

 out a portion of the body wall (ectosome) and examining it as 

 a transparent object with a low power of the microscope. A 

 number of stout longitudinal bands or bundles of large spicules 

 radiate upwards from the peduncle to the osculum, more or 

 less parallel with one another, but sometimes branching. 

 These bundles occur in the innermost portion of the ectosome. 

 They support on their outer surfaces a layer of large, trans- 

 versely, or obliquely disposed spicules arranged in rather con- 

 fused and irregular bands. The spicules of both these systems 

 are more or less parallel with the surface of the Sponge, but 

 we now come to a third system of spicules placed at right 

 angles to the surface of the Sponge, and consequently at right 

 angles also to the other spicules. This third system consists 

 of innumerable tufts or brushes of small spicules (fig. 9,sp. b.), 

 whose apices project from the surface of the Sponge, and whose 

 bases rest upon the spicule bands of the second system. These 

 tufts are placed at a little distance from one another, and, 

 when viewed from the surface, are seen to be arranged in 

 a somewhat reticulate manner, so as to leave certain irregular 

 spaces free from their presence. Within the choanosome the 

 skeleton is very feebly developed, but is not so poorly repre- 

 sented as in Ridleia. It consists chiefly of separate 

 bundles of small stylote spicules, each bundle (fig. 11) being 

 composed of a number of spicules arranged parallel to one 

 another. These structures closely resemble, on an enlarged 

 scale, the well-known ' ' trichite bundles " or " trichodragmata " 

 of some Halichondrine Sponges (e. g. Esperella Murrayi), 

 and I attribute to them the same function as has been attri- 

 buted to the trichodragmata by Mr. Ridley and myself. In 

 our report on the Monaxonida of the " Challenger " Expedition 

 we suggest that these last serve, like straw in mortar, to bind 

 together the soft, gelatinous tissue in which they lie. The 

 trichodragmata are, of course, bundles of microsclera or flesh 

 spicules ; the occurrence of similar isolated bundles of mega- 

 sclera has not, I believe, hitherto been noted. As they are 



