Dr. Bowerbank on Hyalonema mirabilis. 397 
cartilage-pit ; they are triangular instead of leaf-like, and slightly 
incline inwards instead of being erect. 
M. truncata of Searles Wood, from the Coralline Crag, is a 
comparatively large, squarish, and flattened shell, and has long 
cardinal teeth. 
L.—On Hyalonema mirabilis, zn reply to Dr. Gray. 
By Dr. Bowrrsank. 
[In the ‘Annals and Magazine’ for October 1866, p. 287, Dr. 
Gray has published a note “ On the ‘Glass-rope’ Hyalonema,” in 
which he has criticised the short observations on that genus in 
the first volume of my Monograph of the British Spongiade. 
Those observations were never meant to be taken as a history of 
the anatomy and physiology of that curious animal, but simply as 
an introduction to the genus Hyalonema among the Sponges, and 
as a reason for figuring the numerous interesting forms of its sili- 
ceous spicula among those of various other species of Sponges. 
The detailed account of these organs, except as far as it was neces- 
sary to illustrate the specimens selected for figuring, was reserved 
for a paper shortly to be published, and especially devoted to a 
minute investigation of the whole of the organization of the 
animal, including the basal mass of sponge-tissue, the spiculous 
axis, or rope, and its coriaceous envelope, with a view to establish 
the organic unity of these parts as portions of one and the same 
animal. 
The criticisms of Dr. Gray are therefore somewhat premature ; 
and in some respects he has so far misrepresented my opinions 
as to render a reply to his observations necessary. But in thus 
answering his remarks it must be understood that I shall not at 
present attempt to decide the questions in dispute, as to whether 
it be a single animal or two animals, the one parasitical on 
the other, and that I shall reserve the structural proofs and the 
reasonings necessary to such a decision for a paper on the sub- 
ject, which I have long had in preparation and which [ hope 
shortly to be able to publish. 
In page 289 Dr. Gray writes, “Again, the specimens being 
sunk in a sponge that had a flat base by which it was attached 
to some marine body, I concluded that the natural habit of the 
animal was to develope itself in a sponge, so as to support itself 
in an erect position ; and this idea was strengthened by finding 
that the sponge near the part where the coral perforated it was 
of a more condensed and harder texture than the other parts of 
it. I concluded that there was a kind of mutual understanding 
(such as we often find between animals that are parasitic on one 
