PHOLAS. 189 
action never ceases whilst moisture remains in the shells, and 
I think it must be considered as settled, that there is no com- 
munity between the cilia and what are called branchial currents. 
I have at Exmouth repeated all the experiments with the 
mercury on fresh flexible animals; the first were performed 
with rigid specimens from spirit; the results are most satis- 
factory, and I think entitle me to state with confidence, that 
in Pholas there is no communication between the branchial 
and anal siphons. 
Since the above observations were written, I am enabled 
to state, after a prolonged and anxious examination of fifty 
living Pholades, under all the phases of experiment, that nine- 
tenths, if not all the water to bathe the branchiz is admitted 
at the pedal gape, and ejected only by the branchial siphon; 
the anal one alone inhales water and discharges it; and in 
the closed-mantle Solenide, Myade, Lutrarie, &c., as well as 
in the open-mantle Veneres, Cardia, &c., the water is only 
admitted imto the branchial vault at the pedal or ventral 
aperture by the simple opening of the valves, and ejected 
according to the structure of their respective sacs, either by 
the branchial issue alone, as in the Pholades, &c., or, as in the 
Veneres, Cardia, &c., by the two confluent orifices, which are 
in fact but one branchial conduit. 
This discovery and attendant results will finally, I hope, 
dispose of the complicated scheme of some authors, of the 
reception and discharge of the water for branchial purposes 
by cilia and separate siphonal ducts, as it shows what I have 
always advocated, that nature gives access to the water for the 
respiratory apparatus by the simple opening of the valves, and 
causes it to be discharged, when effete, by their closure at the 
posterior siphonal issue, as well as by the pedal opening and 
ventral scissions of the mantle. It is therefore I think satis- 
factorily proved, that the doctrine of separate currents by cilia, 
and that the inhalant is always kept distinct from the exhalant 
current and admitted by a separate aperture from that by 
which the latter is expelled, or in other words, that the water 
is imbibed by the branchial siphon and discharged from the 
anal, is absolutely untenable. 
