BowERBANK^ Oil Gvantia ciliata. 
81 
always more or less of a conical form ; and if we examine 
under favorable circumstances a section of one of these cells^ 
made so as to allow of an oblique view of the inside of its 
conical termination^ the pores may be seen occupying all 
parts of the cone^ and are best observed by the aid of a 
Lieberkiihn and a power of about 150 linear. They are 
rather numerous^ and I have seen four in the space that 
would be occupied by one of the triradiate spicula. The 
outside of the cone is encircled by a number of long, slender 
acerate spicula_, which are firmly cemented to it for a consi- 
derable length of their basal portions, while their apices are 
projected outward. In specimens which are dead, or in a 
state of quiescence, we usually find the terminal cone of the 
interstitial cell considerably elongated and gradually at- 
tenuated at that part of its parietes where the proximal 
ends of the ciliary spicula are attached, and this gradual 
inclination of the side of the cell towards its long axis neces- 
sarily effects a corresponding inclination of the circle of 
ciliary spicula, which has the effect of concentrating the 
whole of their distal terminations at a point considerably 
above the conical end of the interstitial cell, thus forming a 
beautiful hollow cone of spicula for the defence of the pores 
during the state of repose, or of the gentle inhalation sub- 
servient to aeration when pure water only is required to be 
admitted to the interior of the animal. But when the 
vigorous action necessary for nutrication commences, a 
striking alteration in the conditions of all these organs im- 
mediately takes place — the rapid imbibition of the water dis- 
tends the interstitial cells to their fullest extent, and the 
distal terminations (attenuated cones in the quiescent state) 
assume the form of cylinders having hemispherical termina- 
tions, the basal attachment of the circle of ciliary spicula are 
thus brought into the positions of lines parallel to the long 
axes of the cells, and instead of forming a conical shield to 
the porous systems, they now become cylindrical tubes of 
spicula, freely admitting nutrient particles of matter for im- 
bibition by the pores of the sponge. We have thus, by the 
agency of ciliary action, combined with the beautiful adapta- 
tion of the distal portion of the interstitial cell to the pur- 
poses contemplated, an amount of action and reaction fully 
equivalent to that which is eflPected by muscular force and by 
nervous energy in the more highly constituted animals. 
If we now turn from the inhalent to the exhalent system, 
we find a very similar series of beautiful contrivances provided 
for alternate action and repose. 
The normal form of the sponge, as I have before stated, is 
