1869.] DR. J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 81] 
structures, I treated the remaining portion of the specimen by boil- 
ing it in nitric acid, and obtained not only numerous specimens of 
the spicula I have described above, but others of an exceedingly in- 
teresting description, which I shall now proceed to describe. 
The large verticillately spined spicula are very numerous, and ex- 
ceedingly various in their proportions. They are usually more or 
less curved, and vary greatly in size and in the mode of their spina- 
tion: some of the larger ones are acerate; that is, each end termi- 
nates in a well-produced point; others have at one end an irregular 
aggregation of stout spines, while the other is acutely terminated ; 
and in some both ends are crowded with stout spines; and the general 
character of the shaft is that of a cylindrical spiculum. They occur 
in every imaginable stage of development, from extremely delicate 
diameters with the whorls of spines in quite an incipient condition 
(Plate III. fig. 6a) up to the fully developed spiculum (fig. 6 6). 
The number of whorls of spines vary from 9 to 16; one with the 
latter number measured =, inch in length, and the diameter of the 
shaft was ;1, inch. The spines are large, acutely conical, and there 
are seldom more than five or six in each whorl. These spicula must 
have been very numerous and closely disposed in the membrane. 
The two small pieces acted upon by the acid would not have exceeded 
the space of a quarter of a superficial square inch, while the results 
of their dissolution by the acid would cover more than a superficial 
square inch, and in a microscopic field of view ~!; inch in diameter 
I counted as many as twenty-one of them. Under all these circum- 
stances there can be no reasonable doubt of these spicula being those 
of the defensive system of the dermal membrane of the sponge; and 
such spicula are usually found as abundant in the basal membrane 
as in other parts of the dermal system. 
I found also a considerable number of small equiangular or sub- 
inequiangular triradiate spicula with smooth attenuated radii, varying 
in size, from point to point of the rays, from 51, to =45 inch (Plate 
III. fig. 7). Such spicula are usually comparatively few in number, 
and are dispersed irregularly on the surfaces of the dermal or inter- 
stitial membranes of sponges. At the margin of a fragment of the 
sponge from very near the basal attachment, which was mounted in 
Canada balsam in its natural condition, I found the small equiangular 
spicula and little acerate ones (Plate III. fig. 8) imbedded in the mem- 
brane amidst minute attenuato-stellate ones. In this position they 
may therefore be regarded as tension-spicula of the dermal membrane. 
Amidst the other spicula resulting from the dissolution of the 
fragments from the base of the sponge by nitric acid there were 
several fureated attenuato-patento-ternate (Plate III. fig. 9) and 
dichotomo-patento-ternate (fig. 10) connecting spicula. One large 
one of the last-named form measured across its ternate termination 
sy inch; and all of them had large central canals in their radii. 
These spicula appear to vary considerably in size; a smaller one 
measured +1, inch in greatest expansion. There can be no doubt 
that they belonged to the expansile dermal system of the sponge ; 
and the small number of them found may be accounted for by their 
Proc. Zoo. Soc.—1869, No. VI. 
