Pleodorina illinoiensis Kofoid in Britain. 171 
corners will form the posterior row, the dotted cells the penultimate row, and 
the others as marked, x 450. 
Fig. 8. A cell from an antheridial colony, which has just undergone the 
first division towards forming antherozoids, x 600. 
Fig. 9. Antheridium with mature antherozoids, x 600. 
Fig. 10 Free antherozoid plaque, in optical median section, x 600. 
Fig. 11. Presumed young oOspore, showing expressed oil drops, x 360 
cells moved like the hands of a clock from left to right (Fig. 5); only 
very rarely (and always when checked by some obstacle and for a 
very short time) did any of the maturer colonies vary the rotation 
into the opposite direction. Young colonies, while still in the 
gelatinous matrix, a considerable time before emergence, would 
sometimes begin to rotate slowly and with jerks and wriggles, but 
still on the whole in the clockwise direction. It was interesting to 
observe the free colonies, when enmeshed among a few loose fibres 
of cotton wool (which kept off the pressure of the cover-glass), 
“ nosing ” slowly round the borders of the lakelet in which they 
were imprisoned, like an intelligent dog, passing into every bay and 
inlet as if trying to find a way of exit, and always keeping the same 
end foremost except when backing out of a narrow gulf in which 
there was not room to turn. 
The colonies, when mature, measured about 150-200/Ain length; 
they consisted of 32 cells, arranged in five distinct bands or zones, 
the anterior and posterior ones containing each four cells, and the 
intermediate ones eight each (Fig. 1). Rarely a colony with four 
zon«s of only four each was to be seen (Fig. 2). The origin of these 
will be shown later. Each colony was surrounded by (usually) two 
mucous coats of different densities; the inner denser one had a very 
regular ellipsoidal outline, both without and within, while the outer 
coat was somewhat irregular in thickness and sometimes wanting. 
The matrix, in which the cells were embedded, within the inner coat, 
was also gelatinous but less firm in texture. The different layers t 
which varied much according to age, could be seen with great 
distinctness when the living colony was heavily stained with 
diamant-fuchsin ; this stained the inner coat most deeply, and also 
the flagella which were thereby rendered very conspicuous. 
Delafield’s haematoxylin and other reagents were less effective. I 
could not succeed in demonstrating any hexagonal reticulations 
round the cells with the methylene-blue which Kofoid recommends 
for the purpose, until I adopted the expedient of pressing upon the 
cover-glass so as to expel the cells ; then five rows of faintly out¬ 
lined irregular hexagons could sometimes be detected. But this 
