Structure of Marine Sponges. 331 
Perversions of the currents do take place Mena rag o pa 
certain circumstances. Thus Dr. Bowerbank, in h 
on the Vital Powers of the Spo —— Published in s 
Report of the British Association for t dvancement of 
Science for 1856, alludes to an occurrence x this kind, on 
which he observes Hd une 9.) The reversal of the action in 
the osculum in this instance was apparently effected by the 
vigour of the action in the other group of oscula, the whole of 
these organs being more or less connected.” The italics are 
mine. 
On the other hand, Háckel (* On the rene of 
Sponges and cpu Ralesonslip to the Corals,” translated in 
the Annals, vol. , January 1870) mene at p. 9 :— 
“T (with Miklucho) Fees the largest cavity into which 
the canal-system is dilated in the sponge-body, and which 
is usually called the excurrent tube or flue (caminus), as 
the stomach, or digestive cavity, and its outer orifice, which 
is usually called the excurrent orifice or osculum, as the buccal 
orifice or mouth.” 
Marine Sponges. 
The chief part of what I have described in Spongilla I have 
been able to identify in the “ ultimate structure ” of the ma- 
rine sponges, both calcareous and | eilicenus nthe is to say, the 
presence and persistence of the ampullaceous sac, which may 
always be recognized, entire or RE as the case may 
be, in a more or less globular group of spherical monociliated 
Sponge-cells in the living state—and in the dried or wet pre- 
Served state (here of course without the cilium), innumerably 
scattered throughout the mass, and thus presenting the points at 
Which the nourishing-apparatus is situated, just as certainly as 
if this had bean , pee by the testing process of carmine prac- 
tised in Spong 
ere it as poa to keep the marine sponges alive as the 
freshwater SPOREH, no doubt their growth in a watch-glass, 
feeding with carmine &c., and the consequent phenomena 
might also be as VE observed; but the recognition of the 
existence of the Tes die sac, as as all the rest has been 
witnessed in Spongilla, is sufficient. The only wonder to me 
is that what I have stated of Spongilla has not been identified 
by others; itis so eas an to grow this sponge in watch-glasses _ 
from the seed-like bodies 
Siliceous Sponges. 
I first noticed more particularly the ampullaceous sac in the 
marine sponges in December last, viz. in Halichondria simu- 
