294 Dr. J. E. Gray on the Spicules of Hyalonema. 
each of them and forms the mass of them, and that they are a 
part of the community of the Palythoe, and not a mere bundle 
of spicules arising out of the sponge. 
If I understand the theory of those who regard the rope-like 
axis of Hyalonema as the spicules of a sponge, they believe 
that the spicules of the sponge are clustered together in the 
centre of the sponge, and are produced, forming an elongated 
columnar coil, which, according to Bowerbank, is covered 
with a skin forming part of the sponge, and according to 
Professors Brandt and Max Schultze is covered with a coat 
of parasitic Palythow. If either of these theories is true, the 
spicules should be of the same form and structure as the spi- 
cules of sponges, and complete and acute at each end. te 
I have shown that the spicules of the coil are not formed 
as the usual spicules of Sponges, but have their ends, and 
especially their upper or distal ends, always in an incomplete 
state of development, and that they are constantly being 
lengthened by the addition of coats to the end of each of the 
layers of which the spicules are composed. I think we may 
conclude that the spicules are produced or secreted by the coat 
of corium that covers them (and this coat has, I think, been 
most indisputably proved to be formed by the community of 
animals allied to Palythoa), and therefore that the axis is not 
a part of the sponge, but the proper secretion of the Palythoan 
animals. | 
Prof. Max Schultze, though he figures this structure (t. 2. 
f.4 &5), appears not to understand its importance; for he 
compares it to a fusiform spicule with a central spherical 
knob that he found in the sponges which are furnished with 
some spines which are directed towards the centre. But this 
is evidently only a variety (and one I have not seen) of the 
stellate spines figured on tab. 4. f. 2,4, 7,8 & 9, though in these 
the spines on the rays are all directed towards the tips. These 
spinulous spicules are all perfect and acute at the tips, and are 
not truncated and growing at the end like the spicules of the 
coil of Hyalonema. 7 
Prof. Brandt’s figures of the spicules of Hyalonema, on tab. 2. 
f. 12,13,14, & 15, much more accurately represent the structure; 
but it is to be remembered that figs. 12 & 13 represent wrong 
ends of the spicule upwards; that is to say, the slender end of 
the spicule is the one that is immersed in the sponge, and the 
blunt truncated lower end, as it appears in these plates, is the 
end of the spicule that is furthest from the place of attachment 
and which is being extended to accommodate itself to the in- 
creased height of the bark or community of polypes. And 
tab. 4. f. 14 also well represents the coat of which the spicules 
