210 PHOLADIDZ. 
tubes, that is one inhalant and branchial and another ex- 
halant and anal, or by what I term supposititious ones? The 
former position I think I have proved in the Pholades, by 
showing that there is no effective communication between the 
two chambers; and in the Anomie and Ostree, that the latter 
condition of the currents is imaginary, appears to be the 
most correct view. It may therefore be considered that in 
the Bivalves, whatever modification their siphonal mechanism 
may present, all are subject to a general law of the water 
being expelled from the same siphon or channel at which it 
entered, aided by the pedal gape and pedal aperture where 
they exist; and in the Anomie and Ostree, in which these 
organs are rudimentary or entirely wanting, the water is 
simply received and expelled through the ventral range, and 
not by an imaginative inhalant and exhalant regular current, 
effected by cilia. 
The remainder of Messrs. Alder and Hancock’s paper re- 
quires no further notice except a few words on their concluding 
experiment showing how the colouring matters collect m the 
neighbourhood of the buccal aperture. I have observed these 
appearances, but I am of opinion, that in an animal cut up 
from stem to stern, with the so-called in-current, as they 
admit, annihilated, little dependence can be placed on the 
action of the gill-laminz floated in a shallow vessel, to account 
for the colourmg matters seen at its oral termination. And 
I cannot understand the hydro-pneumatic statics of these 
gentlemen, nor the position agreeably to their theory, that 
“a tendency to form a vacuum” in the anal chamber and 
interbranchial tubes is effected by the “flowing out” of the 
water from the ex-current siphon, combined with ciliary 
agency, which actions, they add, are the foundation of their 
“correct answer to this question: How is the matter, divided 
into such minute particles, collected on the surface of the 
gills?” 
But a fallacy with respect to a tendency to form a vacuum 
seems to present itself, as in this case a flowing out involves 
the idea of a flowing in, which militates against the vacuum, 
for the fact is, that with the outflow there is in their theory a 
