120 ~=Prof. W. Thomson on the “ Vitreous” Sponges. 
—an assemblage of the most beautiful, the most singular, and 
the rarest of marine productions. 
GENERAL CHARACTERS OF THE GROUP. 
Condition of the Sarcode. 
From its essential simplicity and the want of any true struc- 
ture, the sarcode of the glassy Sponges cannot be expected to 
afford any very marked distinctions; still even this element 
seems to differ in certain characters from the condition in 
which we find it in the other orders of Sponges. It is small 
in quantity, very soft, probably semifluid, extending in a thin 
layer over the fascicles of siliceous needles and over the sili- 
ceous framework. It appears to contain no trace of the dif- 
fused granular horny matter with which the more consistent 
sarcode of the Halichondrida is so often loaded. When a 
vitreous Sponge is dried (and all the specimens which have 
yet reached Europe are in a dry state), the whiteness of the 
skeleton is barely masked by the pale bs te film which re- 
presents the contracted animal matter. Most of the specimens 
of Huplectella in the market have been bleached; but some of 
them, which may be recognized by their pale fawn-colour, are 
merely dried; and if a portion of one of these be steeped for a 
short time in a warm weak solution of caustic soda, the sarcode 
softens and expands, and may be examined under the micro- 
scope with tolerable success. It is generally almost transpa- 
rent, with here and there scattered endoplasts and minute 
compound granular masses. Among the meshes of the sponge- 
network, and everywhere except where it is extended (as in 
Hyalonema and Euplectella) over the surface of enormously 
long separate needles, the sarcode contains abundance of ex- 
tremely minute spicules, scattered through it singly or aggre- 
gated in groups. ‘These spicules, as we shall see hereafter, 
are often complicated in form and ornament, and are highly 
characteristic of the order and of the several genera. 
The Stliceous Skeleton. 
In Habrodictyon and Hyalonema the skeleton is composed 
entirely of separate siliceous spicules of various forms, inter- 
woven in fascicles and connected by the thin sarcode layer, or 
scattered irregularly among the fascicles of spicules. In Hw- 
plectella, Aphrocallistes, Dactylocalyx, and Farrea, certain 
ing his lovely specimen, upon which Professor Owen founded the species 
Euplectella cucumer. I can have no doubt that this is merely an example 
of £. aspergillum of a rather unusual form, which has attained its full 
size, but in which the raised spiral crests are as yet imperfectly developed. 
