CILIARY MECHANISMS OF LAMELLIBRANCHS 637 
tube. When a sufficient quantity has accumulated, the adductor 
muscles suddenly contract and pressure enough is developed on 
the water in the mantle chamber to reverse the stream in the 
incurrent siphon and throw a jet from it with great force. Being 
in a favorable position, the mantle accumulation is caught up 
and discharged through the siphon tube. 
Except a narrow border on its free edges, the entire inner sur- 
face of the mantle is ciliated, the only function of its cilia being 
to collect matter for removal. Attention is again called to the 
fact that, for some reason, there are times when, even on a large 
ciliated surface, it is very difficult to demonstrate the cilia cur- 
rents. Trouble was experienced in making out the mantle cili- 
ation of Schizotherus at Oreas Island, with light material like 
carmine, while later it was successfully employed at Eagle Island; 
and yet it is not possible that locality had anything to do with 
the matter. Again, when carmine remained stationary, or 
moved feebly, the relatively enormous weight of a whole tea- 
spoonful of sand, thrown on to the mantle, was moved without 
difficulty. Everywhere, too, individual differences in the rapid- 
ity of movement are found, though whenever currents can be 
demonstrated at all, they are apparently always the same in like 
regions. 
Outgoing tracts on the palps. Cilia tracts are much more com- 
plex on the palps than on other organs, not excepting the gills. 
When a quantity of carmine scttles on the faces bearing the folds, 
the rapid twists and turns of particles presents a spectacle of the 
utmost confusion, and it has required a large amount of observa- 
tion to demonstrate positively the hidden uses of individual cur- 
rents. While cilia on other organs move material only toward 
or away from the mouth, the palp cilia perform both these func- 
tions, and the mechanism is so complicated that nervous and 
muscular aid is necessary. It seems certain that the great lat- 
eral extension of the palps, and indeed their entire organization, 
has come about as the result of a demand for more and more per- 
fect ciliary activities. 'They have become the controlling organs 
in feeding and in the removal of objectionable matter from the 
mantle chamber. Except in a very few cases, their action alone 
