348 DR. J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [ May 13, 
hexradiate stellate spicula amidst the sarcode; but the density of 
that substance rendered them almost invisible. 
In some of the specimens that I have recently examined, I have 
observed a remarkable habit of some of the rectangulated hexradiate 
spicula—that is, that one of the axial radii is more or less sheathed 
or enveloped by branches of skeleton-fibre, so as to give the spiculum 
a firm and permanent position; and this appears to be more frequently 
the case with those which are projected into the inhalant areas. 
This attachment of the spiculum by the fibre is not a fusing of one 
into the other, as when two fibres touch each other, but it is simply 
a partial envelopment of a portion of one of the radii, so as to give 
it a secure basal point of attachment to enable it to perform its 
appointed office of sustaining the interstitial membranes of the sponge 
under peculiar circumstances, or to protect the orifice over which it 
is projected. The portion of the ray thus enveloped may frequently 
be traced within the enveloping fibre. It is a very remarkable fact 
that none of the other auxiliary spicula, although large and strong, 
are ever seen to be tlius agglutinated by the fibres. This singular 
habit of the rectangulated triradiate spicula assimilates them in their 
office in some measure to the auxiliary fibres in the skeletons of 
Dactylocalyx and Iphiteon. Although thus agglutinated by the 
fibre, they really form no essential part of the true rigid skeleton of 
the sponge, but are in reality neither more nor less than auxiliary 
supports to the interstitial membranes under certain conditions. 
APPENDIX (May 25, 1869). 
Since the preceding portion of this paper was written, I have seen 
several specimens of Aleyoncellum speciosum that were sent home in 
spirit in the condition they were in when taken from the sea. There 
were five specimens, all as nearly as possible in the same condition. 
They were of a dark dirty colour, and looked very much as if they 
had been dipped into thin mud and then dried. On mounting slices 
from the surface, and fragments of the entire structure of the skele- 
ton, this dirty-looking substance, when immersed in Canada balsam, 
proved to be the remains of the membranous and sarcodous tissues ; 
but I could not find any traces of a dermal membrane, such as might 
naturally be expected to be present if the sponges were in a living 
condition when taken from the sea. The largest specimen in spirit 
had a considerable portion of one side of it entirely deficient of the 
sarcodous and membranous structures that were abundant in the other 
parts of the specimen. This cireumstance, the deficiency of dermal 
membrane, and the condition of the sarcode and interstitial mem- 
branes in the whole of the specimens, appears to lead to the conclusion 
that these specimens were dead sponges in a state of partial decom- 
position, and that we have yet to acquire specimens which were in 
the living state when brought up from the bottom of the sea, 
Although not in so satisfactory a condition as may have been 
desired, they were still in such a state of preservation as to afford 
some interesting points of information regarding the structural pecu- 
