Wager . — The Life-history and 
176 
Structure of the Thallus. 
The thallus is unicellular and uninucleate. The cells vary much in 
form and size, sometimes smaller, but frequently larger than the cells of 
Eiiglena . In form they vary from a nearly spherical to an elongate 
shape and are commonly very irregular in outline (PL XVI, Figs. 1-5 and 
PI. XVIII, Figs. 49 - 55 )- 
The pseudopodia or haustoria which radiate from the cell in all 
directions are prolongations of the cell-body and continuous with it. The 
delicate membrane around them is difficult to observe, but in the later 
stages of development it becomes impregnated by some substance which 
takes up stain, and is then easily seen on staining with fuchsin. Both 
Bail (’ 55 ) and Nowakowski ( 76 ) call attention to the resemblance of these 
haustoria to the pseudopodia of certain Rhizopoda. This is certainly very 
striking, especially in the earlier stages of development ; the young spherical 
cells, with their delicate haustoria radiating on all sides, look exactly like 
some forms of the Heliozoa (Figs. 50-55). 
The protoplasm of the cell is dense and granular, and contains numerous 
oil-drops. The pseudopodia show finely granular contents with minute oil- 
drops. The oil is coloured light brown in osmic acid. 
The nucleus stains very easily in any of the ordinary nuclear stains. 
Cover-glass preparations can be made by lowering a cover-glass gently 
upon the scum at the surface of the water. The scum sticks to the cover- 
glass sufficiently firmly to allow the operation of fixing, staining, and 
mounting to be carried out without any danger of its being washed off. 
Or, a small piece of the surface scum of Euglenae is cut off and floated 
on to a microscopic slide. This is allowed to dry round the edges to 
attach it firmly to the slide, and is then fixed, stained, and mounted. For the 
details of cytological structure, microtome sections from material embedded 
in paraffin in the usual way are desirable. 
The structure of the resting nucleus differs somewhat from the normal 
structure in the higher plants. We find a slightly stainable substance in 
the form of a more or less spherical mass in the centre of the nucleus, but 
connected to the nuclear membrane by delicate radiating threads (Figs. 57- 
62). On one side of this is an arc-shaped cap of chromatin which some- 
times appears homogeneous, sometimes vacuolar, and sometimes granular 
(Figs. 1-5 and 57-62). The slightly stainable mass in the centre looks as 
if it were a much condensed fine network. All the chromatin of the nucleus 
is contained in the arc-shaped mass. Somewhat similar nuclei have been 
described by Percival ( 5 09 ) in Synchytrium endobioticum. Sometimes this 
arc-shaped mass is found in close contact with the periphery of the nucleus 
as shown in Fig. 3, and on passing into the sporangium it becomes flattened 
against it (Fig. 28). In the course of the nuclear divisions which take 
