82 Notes and Comments. 
GRAVITY AND MICRO-ORGANISMS. 
AG a recenL meeting of the Royal Society, Mr. Harold 
Wager read a paper on ‘ The effect of gravity upon the move- 
ments and aggregation of Euglena viridis Ehrb., and other 
micro-organisms. This species, and others, when placed in 
shallow vessels or narrow tubes in the dark, become agere- 
gated into peculiar network-like patterns, or more or less 
well: defined groups. In a narrow tube, placed horizontally 
in the dark, the aggregation takes the form of a series of 
groups W hich look like green bands crossing the tube from one 
side to the other. Each group shews a constant cyclic up-and- 
down movement, the denser central region moving downwards 
under the influence of gravity, and a lighter peripheral area 
consisting of organisms moving upwards, mainly by their 
own activity. The aggregation depends upon the number of 
organisms present, their activity, and the depth of the vessel 
in which they are contained, and may persist with its regular 
cyclic movements for several day s. The downward movement ap- 
pears to be purely a mechanical one, dependent upon the specific 
gravity of the organism, and is not due to a stimulus which 
evokes a physiological response, as in geotropism or geotaxis. 
The upward movement is, on the other hand, due partly to the 
activity of the organisms “Gineiiee ves , partly, no doubt, to the 
upward currents set up in the liquid by the friction of the down- 
ward moving stream. The upward movement of the Euglena 
is more or less vertical, and appears to be controlled, so far 
as the orientation of its elongate body is concerned, by the 
action of gravity. The aggregation resembles the cohesion 
figures produced when fine sediments are allowed, under certain 
conditions, to settle down slowly in a liquid, and are probably ~ 
brought about much in the same way. The movements of certain 
micro-organisms are apparently controlled, therefore, in a 
purely mechanic al fashion by gravity, combined with cohesive 
forces, and this is of advantage to species which, like Euglena, 
are often found in large numbers in a confined space, in that it 
prevents their accumulation in such dense masses as would 
be likely to interfere with their assimilatory and respiratory 
functions. 
ORIGIN OF THE TRIAS. 
At a recent meeting of the Geological Society, Mr. A. R. 
Horwood read a paper on ‘ The Origin of the British Trias.’ 
He pointed out that during the Triassic period in Britain, 
deposition, in his opinion, was brought about solely by the 
action of water, and the British Trias is a Delta-system, for 
during Carboniferous, Permian and Triassic times, deposition 
was mainly in the same area. There is a gradation from the 
Bunter to the Rhetic. The Bunter is known to be of fluviatile 
Naturalist, 
