AND PHTSIOLOGT OF THE SPONGHADiE. 
795 
dispersed without order on every part of their surface. It is the only instance I have 
seen of such an elaborate mode of protection of the porous areas in the Spongiadee. 
In my “ Further Eeport on the Vitality of the Spongiadse,” published in the Reports 
of the British Association for 1857, I have described at length the opening and closing 
of the pores in S^pongilla fluviatilis : each operation is commenced and terminated in less 
than a minute ; they are perfectly dependent on the will of the animal ; and in neither 
case are they simultaneous, but follow in irregular succession,, in accordance with the 
necessities of the animal ; and when once the pores are closed, they do not appear to 
ever open again in precisely the same spot. 
In these wonderful opening and closing operations in the dermal membrane of Spon- 
gilla, every movement is accomplished as systematically and accurately as if there 
were a perfect system of nerves and muscles present, while not a vestige' of [fibrous 
structure can be detected in the thin translucent membrane and its sarcodous lining. 
No cicatrix remains for an instant after closing, no indication is perceived of the spot 
where the opening is the next moment to be efiected. 
In sponges exposed to the action of the atmosphere, between high and low water 
marks, and in dried specimens, the pores can rarely be detected. In the first case 
they are carefully closed on the receding of the tide, that the water within them may be 
safely retained during their exposure to the atmosphere ; and in the latter case the 
violence offered to the sponge, and the shock of its removal from its native locality, are 
sufiicient to induce an immediate closing of those organs, as I have shown in the 
details of my observations on these organs in S])ongilla in the volume of the Reports 
of the British Association for 1857, to which I have before alluded. But should a 
specimen of marine sponge, after a careful removal from its place of growth, be placed 
in a shallow pan of sea-water, and be allowed to die of inanition, it then frequently 
expires with the whole or a considerable portion of the pores open, and in that state it 
may be readily preserved for the cabinet. 
The Oscula. 
The oscula are the fsecal orifices of the sponge. They are situated at the distal termi- 
nations of the single or concentrated excurrent canals of the animal. They vary con- 
siderably in form and size ; sometimes they appear as single large orifices, while at others 
they consist of several small orifices grouped together. When the sponges are massive 
and solid, they are usually to be found dispersed over the dermal surface, but occasionally 
they are grouped on the highest portions or on the elevated ridges of the mass. In 
Geodia Barretti they are concentrated in deep depressions or pits. In other cases they 
are entirely hidden from view, lining the interior of elaborately constructed cloacse 
situated in the centre of the sponge, as in Grantia compressa and ciliata, Verongia Jistii- 
losa, and a numerous series of species of fistulose sponges from the West Indies. 
They are permanent organs, and are capable of being opened or closed at the will of 
the animal, and are subject to a considerable amount of variation in size and form, in 
MDCCCLXII. 5 Q 
