386 Davis . — On Euglenopsis : a Nezv 
Suppose a Euglena in the non-motile condition, and 
therefore enclosed in a cyst, to push forward in a certain 
direction and thus to lengthen the cyst into a filament. Then 
let us imagine this Euglena to encyst itself periodically by 
forming a wall across the filament and occasionally to divide 
in such a compartment. Finally, let the Euglena free itself 
from the filament and pass into a motile condition. Such 
a life-history would be identical with that of our organism. 
The manner in which the inferior ends of the masses of 
protoplasm contract and round themselves off previously to 
the formation of a wall across the filament certainly resembles 
greatly the behaviour of unicellular organisms when they are 
about to enter a condition of encystment. Our organism in 
the quiescent condition is surrounded by a wall, closely 
applied against the protoplasm on every side, enclosing it 
in what may readily be called a cyst. It is also true that 
the masses of protoplasm only divide when they are in the 
quiescent state, that is when they are enclosed in this cyst or 
compartment of the filament. Many unicellular organisms, 
the greater part of whose existence is passed in a motile 
condition, only divide when in the state of encystment. To 
the writer’s mind the behaviour of our form, when passing 
into the quiescent state, fulfils all the conditions of the process 
of encystment. 
It sometimes happened with the zoospores in the aquaria 
that, when they came to rest, the masses of protoplasm did 
not immediately develope into filaments, but divided in the 
cells which enclosed them. Such an example is shown in 
Fig. 9, and here one may readily see that the protoplasmic 
mass has collected at the top of the cell-cavity, or we may 
say cyst, and there divided. Two partitions across the space 
below the mass of protoplasm indicate that the latter paused 
twice before it reached its final position. It is doubtful if the 
zoospores under more normal conditions, that is in their 
natural habitat, behave in this manner, for, from the writer’s 
observations, the tendency of this organism is to immediately 
develope into a filament. However, this unusual behaviour is 
