

T 78 THE NORTHERN MICROSCOPIST. 

have been caused by some force foreign to the diatom. Most of 
my observations have been made on fresh filterings from the water 
of Lake Erie, in which a large amount of flocculent matter was 
present, and in which infusorial life was abundant. 
The common phenomena of the motion of diatoms are well 
described by the Hon. J. D. Cox, in this Journat of April 188r, 
p. 66, and may always be seen in a gathering of diatoms where 
much light matter is present in the water. The same writer gives 
some observations reported by Dr. Wallich as very curious, in the 
JournaL of November, p. 206.* The phenomena reported by both 
the above-named gentlemen have repeatedly come under my 
notice, as well as the growth of the silicious filaments referred to 
by Mr. Mills in the Journat for January,* p. 8; and I have 
observed a similar growth on frustules of Métzschia. From my 
observations, I believe these silicious filaments to be mere adven- 
titious excrescences, like a wart or tumor on the human body ; yet 
I am satisfied that they affect the motion of the diatom on which 
they grow, just as a rudder or centre-board affects the motion of a 
vessel, without any connection with the cause of the motion. In 
one case I observed a very active WMtzschéa having eight or ten of 
these bristle-like filaments, all on one side, one much longer than 
the others, and this frustule moved in curved lines, the filaments 
on the inner side, although ordinarily this diatom has a rectilinear 
course. Presently the long filament became entangled in some 
rubbish, and for a time the diatom swayed back and forth, as on a 
pivot, when suddenly the bristle broke short off, close to the valve, 
and the diatom thus freed moved away to some distance, resuming 
an almost straight course. Since I first saw these filaments on a 
diatom I have frequently recognized them, and doubt not they are 
often overlooked in the fresh gatherings and detached in boiling if 
the gathering is cleaned. By means of such filaments, if very 
small, a diatom might seize and carry along extraneous matter with 
which it came in contact, as it is often seen to do, without the 
filaments being perceived; but this would not account for the 
travelling of particles along the diatom while it is held fast, as so 
commonly happens, 
Many of the phenomena connected with the motion of diatoms 
seem to indicate that the frustules are enveloped in a membrane, 
and such I believe to be the case. This enveloping membrane, if 
adhesive, would cause many of the appearances noted, provided 
the motion be accounted for; but adhesiveness of the diatom 
would not of itself cause motion, I have often seen a small diatom 
moving along beside a much larger, stationary one, cause the latter 
to revolve by the friction, often partly overturning it. But in the 


* American Monthly Microscopical Journal. 

