Wager: Movements of Aquatic Micro-Organisms. 175 
direction of the light is much more irregular than in a stronger 
hght. 
If they are kept in bright sunlight for any length of time, 
they come to rest and round themselves off ; and if they remain 
in a good light for some days, the cells gradually become 
encysted. The effect of a strong light is always to produce 
encyst ment (Fig. IV.). 
Under normal conditions the Eugleme at night round 
themselves off and form a scum on the surface of the water. 
They still exhibit sensitiveness to light however. If a small 
quantity of such a scum is placed in the bright light of an 
IV. — Euglenas in the non-motile vegetative condition. Many of the cells 
are in a state of division. From a photograph taken through l lie microscope 
with a J-inch objective. 
incandescent gas mantle focussed through a substage con- 
denser, many of them again become elongated and move about 
freely in the light space. In this condition they show a 
peculiar response to a decrease in the light intensity. On 
turning the condenser down so as to reduce the light very 
considerably, they at once, in most cases, contract in an 
amoeboid fashion and may become completely rounded off 
again. If the light is then completely cut off, they remain in 
the rounded off condition, but if they are allowed to remain in 
the low intensity of light for some time, they become expanded 
again and move about slowly and sluggishly in the light space. 
If we increase the intensity of the light their movements 
1914 June 1. 
