NOTE ON LAND AND FRESH WATER SHELLS. 327 
frustule at each end alternately, then that must cause a current in the 
water, at the point where the fluid is forced out, and if there isa 
current, it will become visible if the water be coloured with carmine 
or indigo. But even with the best glasses, unsurpassed for clearness 
and definition, and with the water containing the diatoms, coloured in 
the usual way, no current is visible ; therefore no current exists, and 
therefore the motion is not produced by the endosmotic and exosmotic 
action of the cell, and the consequent emission of a fluid through 
minute foramina at the extremities of the valve. 
I must, however, admit that with objectives constructed by our 
best London makers, and after careful observation, I have hitherto 
failed to detect either cilia on the diatom, or a current in the water; 
but the facts I have now submitted, seem to me to be wholly irrecon- 
cileable with Professor Smith’s theory, and to lead to the conclusion 
that these movements are owing to the presence of cilia arranged 
along the exterior of the diatom valve. It must be borne in mind 
that the very small specific gravity of the diatom valve would require 
an extremely slight power to produce all the motion we see, and that 
consequently the cilia, if the motion is so produced, may be so 
extremely delicate as hitherto to have evaded actual detection, but 
that fact is not sufficient to warrant the conclusion that because cilia 
have not been actually seen, therefore, they do not exist.” 
NOTE ON LAND AND FRESH WATER SHELLS COL- 
LECTED IN THE ENVIRONS OF TORONTO, C. W. 
BY A. E. WILLIAMSON. 
(Read before the Canadian Institute, Saturday, Jan. 19th, 1861.) 
I propose, in the following short paper, to give the result of the 
researches of an amateur in one branch of a favourite pursuit, made 
in a somewhat desultory manner and in the intervals of business, 
during which I have managed to collect a tolerably well filled cabinet. 
Among the specimens thus collected, those of the fresh water and 
terrestrial shells comprise a small but very interesting portion; 
