PHOLAS. 197 
impotent motor agents. I have in a former paper expressed a 
belief that the function of the cilia is to beat and subdivide the 
water, that the oxygen may be the more easily extracted. I 
must now observe that all the testaceous Mollusca have many 
parts of their bodies clothed with cilia, which show their action 
in a similar manner to the Bivalves. What then, in them, 
are the functions of these appendages? May we not reason- 
ably conclude, the same as in the Bivalves, to extract air from 
the water not only for their branchiz, but perhaps to pass the 
vital fluid through the pores of the body. One can hardly 
suppose that in either group their duty is mechanically to 
create currents, when a more simple, visible, and effective 
plan exists; I therefore think the view is untenable, that they 
effect the im- and out-flux of water in the anal and branchial 
chambers. I believe a simple hydrostatic law provides for 
this operation in all the Bivalves by a vacuum being formed 
by the contraction of the valves in the expulsion of the effete 
water, and that on opening them and relaxing the siphonal 
orifices to take in a fresh supply the vacuum ceases. 
The action of the cilia is local. That they produce currents 
or rather eddies on the gill-laminz and different parts of the 
body of the Gasteropoda cannot be doubted ; these result from 
every stroke of each that causes a displacement of fluid which 
instantly reverts to its level, but they are not the locomotive 
agents of the entrance or exit of the branchial water ; they 
are strictly particular, having no determinate line of opera- 
tion, and act indiscriminately from every pole. As presump- 
tive proof, examine an oyster or a muscle from a provincial 
stall a few days after they are received, when the cilia under 
the microscope will be found in full action as if just taken 
from the sea, and will continue so as long as moisture re- 
mains. In this case these species, even if they had siphons, 
could’ not produce in- and out-currents by separate ducts, 
from non-access to water; we are, therefore, bound to give 
the preference to the idea that their functions are to eliminate 
the oxygen. I may observe, that cilia are attached to the 
different epithelia in all animals, from the monad to man. 
The inconsistency of such a motive power will be apparent 
