120 Dr Grant’s Observations on the Structure 
depth in the substance of the animal, when the currents are in 
full activity, indicate no difference of temperature. 
Having observed that the structure and disposition of the 
pores, canals, and fecal orifices of the sponge had an obvious re- 
lation to this circulation of water through its body, I could no 
longer doubt that the currents formed one of the living func- 
tions of this animal ; and, as the existence of this living function 
was instantly ascertained, by placing the sponge in sea-water, 
and was so conspicuous as to be visible at the distance of ten 
feet from the animal, I employed it in all my succeeding experi- 
ments, whenever it was of the slightest importance to ascertain 
that my specimens were still alive. As I had already satisfied 
myself that the fecal orifices had no concern with the production 
of the currents, by observing that they continued the same, when 
all the papillae were cut off, and finding it impossible to deter- 
mine, from the discordant statements of naturalists, how far this 
function might depend on the contractile power of the animal, I 
performed several experiments to ascertain the extent of this 
power, in order to compare it with the force of the currents, and 
to observe how far the properties ascribed by the ancients to the 
sponges of the Mediterranean, agreed with those of the species 
now inhabiting the Frith of Forth. 
I first selected a young branch of the Spongia coalita , which 
I judged, from the velocity of its currents, to be in perfect 
health ; and, in order to observe it minutely, and at the same time 
to preserve it, as nearly as possible, in its natural state, I placed 
it in a shallow vessel, with some clear sea-water, in the light of 
the sun. On touching its body smartly with the finger, and ob^ 
serving it for five minutes afterwards, I could not perceive any 
trembling motion of the animal, or any gradual contraction of 
its body ; it did not bend itself to either side, nor could I per- 
ceive any hollow formed at the place touched. When the sur- 
face of the Lobularia digitata is touched with the finger, there 
follows not only a retraction of the polypi, but, the zoophyte 
continuing to contract its fleshy axis* there is a slight hollow at 
length formed on the surface, at the place where the finger 
touched. I now thrust a needle through the body of the ani- 
mal ; and, on withdrawing it, I could not detect, with the assist- 
ance of a lens, the most languid motion of the part, or of the 
