198 PHOLADID 2. 
from the consideration that the cilia must act antagonistically 
from opposite pomts; one set to work the water in bran- 
chially, and another to expel it through the anal duct after 
percoiating the gill-lamine and interbranchial tubes. I shall 
recur to the cilia, and expect to prove that the new scheme of 
communication between the two siphons is very problematical, 
I may say impracticable. 
Messrs. Alder and Hancock go on to say, that any one 
may convince himself of the existence of a branchial -current 
and an anal ex-current, by placing a Pholas “in a glass of 
sea-water, and then by gently adding a little fresh, slightly 
charged with floating particles,” the two actions may be per- 
ceived. I admit, by this process, that currents will ensue, as 
the invigorating fresh element causes the animal to expel that 
which has become effete and take in a new supply; but as I 
have, under every condition of experiment, examined multi- 
tudes of these creatures, I am bound to declare that the 
currents have no continuous regularity : and I think the mode 
of testing thei presence by means of water charged with 
buoyant particles is fallacious ; these only float on the sur- 
face, and are subject to many perturbations and deceptions 
arising from depth of water, currents of air, the position of 
the animal, whether on the ventral or dorsal surface, by its 
will and humour, state of exhaustion, and an unnatural con- 
finement. My repeated examinations show that the parti- 
cles are whirled in all directions ; sometimes they pass ito 
the branchial chamber, at others none will enter: capricious 
‘gyrations, whether arismg from the action of the animal or 
other natural causes, are their ruling character. With respect 
to the anal siphon, the floating particles are certainly repelled 
from its orifice in a somewhat regular and continuous manner, 
being only interrupted by the periodic reception of fluid to 
supply the exhaustions. The frequent repulsions of particles 
from the anal orifice have been construed by Messrs. Alder 
and Hancock to arise from the percolation of water from the 
branchial vault through the gill-lamine and interbranchial 
tubes to an issue at the anal siphon, produced by the agency 
of cilia. I think it will appear that this complicated operation 
