Mr. J. Alder on the Animal of Kellia rubra. Dil 
long siphons (Mya, Lutraria, &c.), the branchiz, being situated 
at a great distance from the apertures, may require from time 
to time the assistance of muscular contraction for a thorough 
cleansing out of the branchial cavity, and in this case the water 
will be discharged out of both siphons from the stronger force 
overcoming the action of the cilia*. 
Mr. Clark takes some pains to prove that the water does not 
make a circuit through the intestines, which position, being un- 
disputed and apparently unconnected with the argument, I should 
not have noticed but for the conclusion drawn from it ; which is, 
“that the water therefore” (on account of not passing through 
the intestine?) “for the branchiz and sustentation must pass 
into the great branchial cavity, and issue therefrom by both the 
ducts at which it entered.” Now is this ? The conclusion appears 
to be a non sequitur: but possibly I may misunderstand the 
meaning of the paragraph, though I have read it over carefully 
more than once. 
With respect to my statement of having seen, under the mi- 
croscope, a continuous current of water flowimg into the anterior 
tube of Kellia rubra, Mr. Clark observes, “ All must admit this 
fact: as the fold is a part of the open mantle, no microscope is 
here required, as in every open-mantled bivalve of adequate size 
this action is instantly made apparent by a common lens, and is 
the invariable result of the animal opening its valves.” In Mr, 
Clark’s former letter he says, ‘ No currents, at least branchial 
ones, enter therein or issue therefrom ; it is a fold merely sub- 
servient to locomotion.” The flow of a continuous current into 
this tube-like fold is now treated as an admitted fact, requiring 
no microscope for its demonstration ;—but it is attributed to the 
opening of the valves. It may be necessary therefore to state that 
the operation goes on when the valves are perfectly at rest, and 
cannot in that case be produced by their means. That I could 
see a current passing out at the posterior aperture is however to 
Mr. Clark a matter of the “ gravest difficulty,” only to be got 
over by supposing that I was deceived by the “aberration and 
well-known great deceptions involved in the use of high micro- 
scopic powers.” It will be a satisfactory answer to this to state 
that I was able to see it with the lowest power of my microscope, 
where there could be no aberration. The advantage of a micro- 
scope over a pocket-lens im this case is the greater facility it 
affords in managing the light, which requires to be transmitted 
* The internal surface of these siphons is usually (perhaps aiways) covered 
with vibratile cilia, more minute than those of the branchiz, but acting in 
conjunction with them in producing the currents. Mr.Cocks informs me that 
he can see the cilia inside the anterior tube of Kellia suborbicularis, with a 
lens of 41-inch focus. 
4* 
