Brae her. — Observations on Euglena deses. 105 
measuring the distance down the slope over which the organisms are to be 
found one is able to calculate the greatest distance to which they burrow. 
As a result it was found that the greatest depth was about \ inch, while 
the majority were found at about | inch. This agrees with the results 
obtained in the previous experiment, and also with that obtained by Laurie 
for Amphidinium , which he says burrows to a depth of about Jinch (6). 
Climatic Conditions. 
(1) Rain. Several visits paid to the Avon during wet weather show 
that E. deses does not appear on the actual surface of the mud during rain. 
If, however, one examines the sides of the small drainage channels which 
Fig. 9. Showing position taken up by Euglenae on the mud during rain. 
run through the mud at right angles to the river, one can see a large number 
of Euglenae clustered here to obtain shelter from the rain, and it is a note- 
worthy fact that they occur in far greater numbers on the side from which 
the rain is driving and so are almost in complete shelter. A section draw- 
ing is shown in Fig. 9. 
( 4 ) Drought. The mud at the outer edges of the river bank often 
becomes very dry when the tide does not cover it for some days, and in 
order to see the effect of drying on the organism, mud was kept in dishes 
and left until quite dry and hard. 
On examination it was found that all the Euglenae were dead and 
disorganized. 
Other mud was kept until it became very stiff but was still soft enough 
to receive an impression. With this the Euglenae ceased to respond to the 
stimulus of light and remained on the surface of the mud. They appeared 
rounded off and dark green in colour. On subsequent wetting the organisms 
yviiD- 
□ 
ram 
mud 
Position of 
Euglena 
