1875.] DR. BOWERBANK ON SILICEO-FIBROUS SPONGES. 903 
5. A Monograph of the Siliceo-fibrous Sponges. By J.S. 
Bowersank, LL.D., F.R.S., F.Z.S., &c.—Part IV. 
[Received June 8, 1875.] 
(Plates LVI. & LVILI.) 
Further observations on the anatomy and physiology of 
ALCYONCELLUM SPECIOSUM, Quoy et Gaimard. (Plate LVI.) 
Euplectella aspergillum, Owen, Trans. Zool. Soe. iii. p. 203. 
Euplectella cucumer, Owen, Trans. Linn. Soe. xxii. p. 17, pl. 21. 
In my former observations on the anatomy and physiolog y of this 
singular and very beautiful Sponge, published in the Society’s ‘ Pro- 
ceedings’ for 1867, p. 351, and for 1869, p. 346, I have stated that I 
had tried in vain to obtain a knowledge of the dermal structures of 
this sponge. In my paper of May 13, 1869, I detailed my exami- 
nation of a very small fragment of what appeared to me to be the 
dermis ; and subsequent examinations of other minute pieces of a 
similar description have confirmed the opinion I had then formed. 
Since 1869 I have made every possible effort to solve the problem 
of its dermal structure, but without any satisfactory result. What 
my best efforts could’ not attain, the good fortune of my friend Dr. 
John Miller, F.G.S. &c., has achieved by the acquisition of a spe- 
cimen in which the skeleton of the dermal organization is in a per- 
fect state of preservation ; and [ am much indebted to him for having 
kindly presented me with part of this beautiful and valuable specimen 
for examination and description. No portion of the sarcodous 
structures remain on any part of the specimen. These tissues ap- 
pear to have been removed from the dermis by gradual undisturbed 
decomposition, leaving its siliceous skeleton iv situ in a remarkably 
perfect state of preservation; and not only so with regard to the 
dermal skeleton, but the rigid skeleton of the sponge appears to be 
precisely in the same state as when living, every portion of it ap- 
pearing to occupy its appropriate position, so as to enable us to 
render a much more correct account of its general structure. Hitherto 
the only specimens available for examination have been in such a 
well-washed condition as to render it extremely difficult to deter- 
mine the true positions of the unattached spicula found among those 
of the rigid skeleton; and in many cases the rectangulated sex- 
radiate spicula of the dermis and the floricomo-sexradiate ones have 
evidently been washed into the interstices of the rigid skeleton. 
On examining a portion of the sponge presented to me by Dr. 
Miller, mounted in Canada balsam, with a power of 100 linear, we 
find that at the inner surface of the specimen the large primary 
fibres of the skeleton are strikingly distinct ; and in the irregularly 
shaped interstices of their reticulation there were numerous stout 
rectangulated sexradiate spicula, and a large number of the same 
form of various degrees of tenuity ; their positious were mostly un- 
