94 Br acker . — Observations on Euglena deses. 
By examining small quantities of the mud under the microscope, one 
can see that the green colour is due to the presence of a vast number 
of small green organisms, identified by the aid of Dangeard (3) and 
'Wager (7) to be Euglena deses. The yellow and brown colour is due 
to the presence of a large number of diatoms, and it is a noteworthy 
fact that while the Euglenae occupy, for the most part, the higher positions 
on the ridges of mud, the diatoms are usually to be found in the damper 
mud of the holiows. 
According to Dangeard (4) Euglena requires a certain amount of 
organic matter for its nutrition, and the occurrence of the organism in so 
great abundance here is probably due to the quantity of sewage brought 
down to the Avon from the neighbouring towns. An analysis of the mud 
at this spot shows that the organic content is 6 per cent, (approx.). 
By continuing observations on the banks of the Avon, one may see 
that the green colour mentioned above is not permanently on the mud, but 
disappears and reappears apparently according to the times of sunrise, 
sunset, and high tide. One may well compare the behaviour of this 
organism with that of Convoluta roscoffensis described by Gamble and 
Keeble (5) and Georges Bohn (1). This animal is found on the shores 
of Brittany, where it colours patches of the sand bright green. It 
comes to the surface during certain times of the day, but burrows into the 
sand during darkness and for the periods of high tide. Laurie (6) describes 
similar diurnal movements in the Peridinian, Amphidinium opercidatum , 
which is brown in colour and occurs on the sea-shore at Port Erin. 
Bohn (2) further shows that certain Gasteropods, such as Littorina 
rudis , exhibit diurnal migrations, taking shelter under pebbles and rocks 
during darkness and high-tide periods. 
Although such comparisons are of great interest, one should remember 
that in all the organisms mentioned above, with the exception of the Peri- 
dinian, there is a much more highly developed structure than in the unicellular 
Euglena , and therefore it is not wise to lay too great a stress on their 
similarities and differences. 
This paper was, therefore, undertaken with a view to investigating the 
possible influence of such external factors as light, tidal flow, and tempera- 
ture changes upon the movements of E. deses and the part which they play 
in the life of the organisms. 
E. deses is very contractile and constantly changing its shape. By 
a series of changes, consisting chiefly of contraction into a ball, expansion 
to full length, and bending round upon itself, the organism is able to creep 
about over the surface of the mud. Up to the present time no cilia have 
been observed, and in the experiments performed the organism appears to 
be unable to swim freely in water. One would expect, therefore, that any 
response to stimuli which the organism makes would of necessity be much 
