68 DR.J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, 
effort to test its accuracy, as it appears to me to be impossible that 
the fibres of Dactylocalyx pumiceus should be seen beneath a micro- 
scopical power of about one or two hundred linear without the con- 
viction being immediately arrived at that the tissue was purely 
fibrous; and sections at right angles to their axes at once exhibit 
their concentric structure, and prove that they are not compound 
structures formed of “separate siliceous spicules of various forms, in- 
terwoven in fascicles.’’ This description, quoted from Prof. W. 
Thomson’s paper (Ann. & Mag. Nat. Hist., Feb. 1868, p. 120), will 
apply correctly enough to Hyalonema, but certainly not to “ Bw- 
plectella, Owen, Aphrocallistes, Dactylocalyx, and Farrea,’”’ the 
latter four genera having purely siliceo-fibrous skeletons, while 
Hyalonema is as purely a spiculo-reticulate structure. 
Prof. Wyville Thomson, in his paper in the ‘Ann. & Mag. Nat. 
Hist.’ for Feb. 1868, has proposed a new name for the siliceo- 
fibrous sponges; but a new name, unless it be more significant 
than the old one, is a detriment rather than an advantage to science. 
He designates them as vitreous sponges; this is an erroneous idea, 
inasmuch as the fibres are not inorganic and amorphous in their 
structure like fibres of glass, but, on the contrary, they are highly 
organized, consisting of concentric layers of silex and keratode com- 
bined, and thus are totally different in their origin and structure from 
an artificial amorphous structure like glass. The term vitreous 
naturally supposes an origin and a transparency through the agency 
of fire; but if we submit the fibres of Dactylocalyx pumiceus to the 
action of that element by making a small portion of the rigid ske- 
leton red-hot two or three times in the flame of a spirit-lamp, it 
comes forth from the trial as black as charcoal, and perfectly opaque. 
If the term vitreous is meant to represent the general character 
and appearance of these sponges in their natural condition, it is then 
still more inappropriate, as in the living state their external ap- 
pearance is that of an ordinary sponge entirely enveloped in a more 
or less fleshy dermal envelope; if at all applicable, it can only be so 
when the animal is in a deteriorated and partially decomposed condi- 
tion; while siliceo-fibrous is correctly expressive of the nature of their 
structure, and contrasts well with the terms kerato-fibrous and 
spiculo-fibrous. For these reasons, therefore, I feel under the neces- 
sity of rejecting the new designation proposed by the learned Pro- 
fessor. 
Prof. Wyville Thomson, in his proposed arrangement of the 
Spongiade “ Order I. (P. silicea) Vitrea,’’ gives the following as the 
characters of his proposed new order :—“ Sarcode in small quantity, 
very soft; never containing formed horny matter, either fibrous, 
membranous, or granular. The skeleton consists entirely of sili- 
ceous spicules, either separate (in fascicles or scattered) or anasto- 
mosing, and combined into a siliceous network. The sarcode con- 
tains small spicula of a different character from the general spicules 
of the skeletons, and of complicated forms. The spicules, whether 
of the skeleton, or of the sarcode, may all be referred to the hex- 
radiate stellate type. Ex. Hyalonema, Dactylocalyx.” 
