ill!Ill

Fig. 4.
Navicula viriais.
A. Valve or valve face.
B. Girdle or zonal face.
HISTORY OF DIATOMS.
2. Movement of Diatoms. A large
number of diatoms, especially those which have a
naviculoid form, are endowed with the power of
locomotion, the cause of which is not yet ascer-
tained, and which has exercised the imagination
ot a large number of observers.
Of the numberless hypotheses which have been
put forward to explain the motion of diatoms, that
which has been advanced most frequently is the
supposition of the existence of cilia this is also the
;
suggestion of Mr. Jacob D. Cox, of Cincinnati,
one of the most learned diatomists of our
age, in a small work ( J ) recently published by
him. Mr. J. D. Cox believes that the raphe is
the seat of a line of cilia, which act in the
groove formed by the raphe, and which Prof.
H. L. Smith declares to be a genuine cleft. The
narrow line of epidermis at this spot being covered
with active cilia, one can easily understand,
says Mr. Cox,
that the formation of silica on
this line would be obstructed or hindered. Still
more recently Mr. O. Biitschli, ( 2 ) Professor of Zoology at Heidelberg
University, has revived the idea of a cilium or very fine flagellum, and
thinks that by means of it the phenomenon
under consideration can
be explained. Unfortunately, up to the present no staining re-agent
whatever has been discovered which will throw these filaments into
relief so that their existence has never been demonstrated.
Professor H. L. Smith has for a Ions; time studied the motion of
diatoms with great care. We cite below a passage from a letter, in which
this scientist describes some interesting phenomena which he was able to
observe during the movement of certain diatoms.
" If a living Finnularia is followed under the microscope
after the field
has been coloured blue by indigo, and when the valve side is in view,
that is to say, with the median line turned towards the eye, small particles
of indigo will be observed to move along the whole length
of the
median line, and then to accumulate near the centre in the form of a
small ball or sphere.
(') Diatoms, their nutrition and locomotion, by Jacob D. Cox, in The Microscope, July, 1890.
2
( ) Mittheilung iiber die Bewegung der Diatomeen. Heidelberg, 1892.