254 BARKAS, ON BACILLARIA CURSORIA. 
continuous line their entire length, and then as rapidly re- 
turn in the opposite direction. 
The cause of the motions of B. cursoria is still a vexed 
question, and I must confess that no theory yet propounded 
at all touches the solution of their mysterious movements. 
They move more rapidly and spasmodically than any other 
diatom. Dr. Donkin, in p. 16 of Vol. VI, ‘Quart. Jour. Mic. 
Sci.” observes that he has only seen B. cursoria in one 
aspect, and he has fallen into the error of describing the 8. V. 
as the F. V. I have several prepared slides in which both 
views are well exhibited, and that which the doctor describes 
as F. V.is 8. V., the F. V. being broader, without median 
line, and with rows of puncte on each side. 
Dr. Donkin observes (‘Quart. Jour. Mic. Sci.,’ Vol. VI, p.18), 
“Whether the filament is at first attached, and afterwards 
Sree, as in B. paradoxa, I eannot positively decide, although 
I believe it to be free, owing to its only occurring in the 
shallow furrows on the beach, where there is not a single 
vestige of vegetable life, except the free species of diatoms with 
which it is mixed.” I have found it frequently on the open 
beach, but never in such large numbers as in the pool at the 
mouth of the Tyne, and the habitat is surrounded by rocks 
densely covered with algze. This fact shakes the inference ex- 
pressed by Dr. Donkin. They may originally be attached species. 
I shall be glad to forward living specimens of B. cursoria to 
any microscopist in exchange for diatoms not obtainable in 
this locality. Since writing the foregoing I made another 
gathering from the same pool, on Tuesday, June 13th, 1865. 
The weather had been fine and bright for several days, and I 
expected to find Diatomacez very abundant. I was disap- 
pointed, as the gathering consisted of a few groups of B. cur- 
soria, and a sprinkling of Pleurosigma and Navicula. On ex- 
amining this gathering of B. cursoria, I witnessed another 
feature in their movements which I had not before observed. 
Two frustules, which were detached from a larger group, in- 
stead of sliding backwards and forwards as before described, 
rolled from side to side, as though one end were fixed upon a 
pivot ; and the remarkable phenomenon to which I desire to 
direct attention is this, that the small gritty particles on one 
side of the right-hand frustules moved freely backwards and 
forwards, in a hurried manner, along the edge of the frustule, 
as though they were occasionally driven by cilia, or as if 
they had automatic or voluntary motion. I observed that 
they moved when the diatom remained stationary. 
