122. Prof. W. Thomson on the “ Vitreous” Sponges. 
many cases several are partially united together. In Huplec- 
tella perfect and distorted spicules of this class are entangled 
in the loose meshes of a framework which is evidently formed 
by the still further distortion and anastomosis of spicules of 
the same type. In Aphrocallistes (see woodcut) the network 
is still more evidently produced by the coalescence of stellate 
spicules, though their haxradlate character is somewhat ob- 
scured. In the network of arrea (Bowerbank, Brit. Spong. 
vol. i. fig. 277) the hexradiate type is very marked. The 
primary axis of the spicule is reduced to a conical. tuberculated 
spine; and spines of exactly the same form are developed in a 
corresponding Seg on the outer surface of Aphrocallistes 
(woodcut, e), Farrea the spicules are distinctly tubular ; 
but this is merely a question of degree. In Dactylocalya 
the reticulation has become very irregular; but I have no 
doubt, from the style of netting (see Bowerb. Brit. Spong. 
vol. i. fig. 275) and from the close analogy in other respects 
between this genus and Aphrocallistes and Farrea, that its 
fundamental te is the same. 
I believe that it would be safe to accept the generalization 
that the continuous siliceous network, wherever it occurs in 
the vitreous Sponges, is produced by the fusion of spicules of 
the hexradiate type. 
Throughout the whole order the spicules of the sarcode are 
very abundant, and are often very elegant in form. They are 
extremely minute, usually not more than ‘001 of an inch in 
length or diameter, and are seen adhering in groups to the 
larger spicules, or entangled in multitudes among the fascicles 
saa. in the meshes of the sponge. However complex these 
spicules may finally become, they all, with ie one doubt- 
ful exception—the bihamate spicule figured by Bowerbank as 
from Farrea occa (Brit. Spong. vol. i. fig. 114)—may evidently 
be referred to the hexradiate type. In both species of Habro- 
dictyon the most common sarcode-spicule is the “ floricomo- 
hexradiate” of Bowerbank (Pl. IV. fig. 1 e); and the same 
form occurs abundantly in Luplectella aspergillum. The 
“‘ coronato-hexradiate stellate ”’ Fores figured by Bowerbank 
(Brit. Spong. vol. i. fig. 195) seems to be the central star of 
one of these without the curved processes. Associated with 
this type, we have in Habrodictyon multitudes of extremel 
minute hexradiate spicules, variously armed and feathered, 
and scarcely distinguishable from the ordinary spicules of the 
sarcode of Hyalonema. The spicule which in the series de- 
parts most from the hexradiate form is the wonderful double 
grapnel of Hyalonema ; but, although its ends are split up into 
curving flukes, in the very middle of the shaft the cross-canals 
