382 Davis . — On Euglenopsis : a New 
base of the plant an empty compartment, and at the top is 
the green protoplasmic mass surrounded by a wall that is con- 
tinuous with the wall below. Often a second cross-wall is 
formed, above the first and very close to it. It is as if the 
mass of protoplasm had contracted from below, after the first 
cross-wall had been formed, and developed a new wall at the 
point of farthest contraction. The writer never noticed more 
than two cross-walls above the first empty cavity, but one 
may often find three or even four such walls between empty 
cavities in upper portions of adult plants. In Fig. 1 may be 
seen several instances where more than two cross-walls are 
present between empty compartments. 
The mass of protoplasm probably remains inactive for 
a short time after it has formed a wall separating itself from 
the empty space below, but very soon it begins to push upwards 
again, and the membrane in which it is enclosed elongates. 
The manner in which this elongation takes place is precisely 
like that in which the original wall that enclosed the zoospore 
lengthened. The mass of protoplasm keeps in the upper 
portion of the cavity, and the lower portion is left empty, and 
then, when the filament has so increased in length that the 
empty space is about equal to the protoplasmic mass, there is 
formed another cross-wall, and another empty compartment 
has been added to the filament of the plant. In Fig. 8 may 
be seen a specimen in which there is the empty cavity at the 
base of the plant, and above the green protoplasmic mass 
surrounded by a wall, and between the two may be seen 
a slight space showing that the upper cell has already begun 
to elongate. 
The writer observed many young plants, which had de- 
veloped from zoospores in his aquaria, until they consisted of 
a filament of several empty cell-cavities with the green cell at 
the free end, and there could be no doubt but that each empty 
cell-cavity was formed in the way just described. The fila- 
ments, therefore, increase in length by the periodic forward 
growth of the masses of protoplasm at their free ends. The 
periods of forward growth alternate with periods of rest in 
