CALYCOSILVA CANTHARELLUS. 73 



tudinal rhabds. On reaching the body proper of the sponge this hollow sheaf 

 of rhabds opens out in a calyculate manner and divides into numerous rhabd- 

 bundles (Plate 5, figs, le, 4e, 16), which extend in the floor of the subdermal 

 cavities paratangentially and more or less radially towards the margin of the 

 plate-like sponge-body. Occasionally anastomosing they here form a kind 

 of loose paratangential network with radially elongated meshes. 



On the gastral side, in the floor of the subgastral cavity, a similar network 

 of preponderantly radially extending rhabd-bundles (Plate 5, figs. Ic, 4c) is 

 observed. 



Besides these paratangential rhabd-bundles in the floors of the subdermal 

 and subgastral cavities numerous isolated rhabds and loose bundles of them, 

 situated obhquely or transversely (Plate 5, figs. Id, 4d), are found in the choano- 

 some. The ends of many of the transverse rhabds adhere to proximal rays of 

 hypodermal and hypogastral pentactines. In the centre of the sponge-plate, 

 near its junction to the stalk, some oblique rhabds, similar to these but very 

 much larger, have been observed (Plate 5, fig. 16). 



At the point of junction of the stalk to the body proper of the sponge some 

 long and slender diactines with actines enclosing an angle of about 90° (ortho- 

 monaenes) have been observed in C. c. var. helix. 



The hexactines lie scattered rather irregularly in the choanosome. The 

 thickness of their rays and the size of their spines are subject to considerable 

 variations. The shortest rayed and most strongly spined are found in the 

 centre of the body at its junction with the stalk. Towards the margin of the 

 sponge-plate the rays of the hexactines become more slender and less spiny. 



Tetractine and triactine hexactine-derivates have been found in small 

 numbers, chiefly in C. c. var. megonychia. The diactine hexactine-derivates 

 are not numerous, and have been observed only in C. c. var. simplex in the 

 region of the junction of the stalk to the body proper of the sponge. 



The gastral and dermal surfaces of the body proper and the surface of the 

 stalk are uniformly covered by a dense pinule-fur (Plate 2, figs, la, 8a, 13a; 

 Plate 4, figs. 21-24; Plate 5, figs, la, g, 4a, g, 11a, g, 16a, g). The two kinds of 

 pinules, with long, well-developed, and pointed proximal ray, and with short, 

 rudimentary, rounded proximal ray, which are not, or hardly at all, connected 

 by intermediate forms, are quite indiscriminately scattered, and although the 

 former are relatively more numerous on the body and the latter predominate on 

 the stalk, both kinds appear every^vhere to be intermingled. Apart from the 

 dermal pinules of the body being on the whole slightly larger and having slightly 



