1869.] DR. J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 71 
the membrane, while their shafts are freely suspended in the interval 
existing between the dermal membrane and the surface of the rigid 
skeleton ; so that when the animal is actively inhaling or exhaling, 
the expansile dermal system expands or contracts in accordance with 
necessities of its vital actions; but when in a state of inaction or re- 
pose, it subsides on to the rigid surface of the skeleton, and the long 
shafts of its connecting spicula are immersed in its interstices. This 
singular and beautiful provision of nature prevails in all the known 
siliceo-fibrous sponges which are in the condition they were when 
alive in their native element ; it also readily accounts for the naked 
skeleton-like structure of many of the specimens of Dactylo- 
calyx and Iphiteon which are preserved in the museums of London 
and Paris. The whole of this beautiful dermal structure is held to- 
gether in life by the tough and elastic dermal membrane; but as 
soon as this is removed, either by decomposition or maceration in 
water, the remainder is the skeleton only of the animal, with pro- 
bably a few of the retentive and interstitial spicula entangled in the 
interstices of the skeleton. I have not seen one of these sponges 
taken from the sea; but in two specimens in my possession, which 
were dried in the living condition, Dactylocalyx Prattii and Masoni, 
their external appearance is that of being enveloped in a thin brown 
leathery or parchment-like skin, and not the slightest indication of 
the beautiful rigid siliceo-fibrous skeleton is visible. In D. Prattii 
the expansile dermal membrane in its present condition is contracted 
into folds and ridges at the margin of the sponge, strongly indica- 
ting its lax and expansile nature when in the living state. I im- 
mersed one end of my specimen of D. Masoni in water for about half 
an hour; on removing it from the water, the dermal surface pre- 
sented a smooth and slightly glazed appearance, and the membrane 
was readily removeable by the point of a penknife from the mass of 
the skeleton. When thus removed, I submitted it, immersed in 
water, to a power of 108 linear; I found that the sarcode lining it 
was so abundant and so much expanded by the water it had imbibed, 
that I could not see the apices of the numerous connecting spicula 
imbedded in it, their long shafts only being visible on its inner sur- 
face projecting through the stratum of sarcode. A thin slice of the 
rigid skeleton prepared under the same circumstances presented si- 
milar difficulties ; the siliceous fibres were completely obscured by the 
abundance of the sarcode present, which filled all the interstitial 
cavities, appearing like a firm gelatinous matter of a deep-brown 
colour ; and it was not until the specimens under consideration were 
dried, the sarcode again contracted into comparatively a thin film, 
and the specimens mounted in Canada balsam, that any of the sili- 
ceous structures of the sponge could be rendered distinctly visible. 
This abundance of the sarcode and its capability when in the dried 
state of imbibing water with great avidity are not peculiar to the 
siliceo-fibrous sponges; a great number of the Halichondroid 
sponges, under similar circumstances, present precisely the same 
phenomena. 
If we make sections in the dried state of either of the sponges 
