IOO 
Br acker. — Observations on Euglena deses. 
a zone always under tidal influence, it was noticed that, although removed 
from the Avon and placed in a dish in the laboratory, the organisms still 
continued to burrow into the mud at the time of high tide. 
In order to ascertain exactly how long this phenomenon persisted, 
accurate readings were taken at every hour by means of the colour scale 
used in the previous experiment, and curves drawn in order to show the 
behaviour of the organisms when removed from the influence of the tide 
(Fig- 5)- 
Fig. 5. A graph drawn to illustrate the behaviour of E. deses when removed from the influence 
of the tide. The lettering and shading are as in Fig. 4. 
The material was obtained at 9 a.m. on Wednesday morning, when the 
mud was well covered with Euglenae. It was placed in the laboratory and 
left without any tidal influence. 
Result. 
On Wednesday afternoon the organisms went down during the period 
of high tide. 
On Thursday afternoon the organisms again went down at about the 
same time as the period of high tide on Wednesday. 
On Friday the organisms again went down for the same period, though 
they commenced to do so about an hour later, the disappearance being 
more rapid. 
On Saturday and Sunday, however, the Euglenae did not disappear at 
all during the day until just before sunset. 
Therefore, although removed from tidal influence, E . deses continues 
to show tidal periodicity for about three days. Gamble and Keeble (5) 
describe a similar periodicity in Convoluta , which they maintain only lasts 
for one day. Bohn (1), however, states that he has watched the phenomenon 
during fourteen consecutive tides. 
Further Investigations of the Influence of Light and 
Temperature on the Behaviour of E. deses . 
The influence of light. It has been shown that E. deses is sensitive to 
light, since it comes to the surface of the mud as soon as the daylight has 
reached a sufficient degree of intensity. Small variations in the light during 
