INTRODUCTION. 
3 
produced abundant swarm-cells in twenty-eight hours, after three 
years and nine months from the date of collection, and in a few 
days all the spores appeared to have germinated, and plasmodia 
were formed in a moist chamber. Sporangia were developed 
eleven days after the sowing of the spores. The spore-wall is 
ruptured by the swelling of the contents, which slowly emerges 
through the opening, and in about ten minutes lies as a nearly 
pellucid globule by the side of the empty membrane; after 
remaining quiescent for a few minutes amoeboid movements begin 
to take place, and shortly afterwards the flagellum is produced. 
This Ls at first a somewhat tentative process, and the flagellum 
is frequently withdrawn ; but in about a quarter of an hour it 
acquires its full length of about 15 /a, and by its lashing strokes 
the swarm-cell swims oif with a dancing movement. At this 
stage it is pyriform in shape, the interior body-substance is 
gi-anular and contains a con- 
tractile vacuole, and often one 
or more vacuoles in addition 
which do not usually show con- 
traction. At the narrow end 
is placed the nucleus, which 
can easily be recognised by its 
lighter and more homogeneous 
appearance and central nucle- 
olus. The nucleus does not 
alter its position, though con- 
stant movement is observed 
among the constituents of the 
granular part. The whole is 
enclosed by a layer of hyalo- 
plasm devoid of granular par- 
ticles, and of extreme tenuity 
over most of the su^rface, but 
thicker at the anterior end, 
where it is produced into the 
flagellum immediately in front 
of the nucleus, and also at the 
posterior end, where it often 
extends in a brush of two to eight more or less slender pseudopodia. 
In addition to the dancing motion, wliich is maintained as long as 
they are free in the water, the swarm-cells when they come to rest 
exhibit movements of an amoeboid character, and spread with an 
irregular outline ; or they assume a linear form and creep over a 
level surface with a snail-like motion, the flagellum being extended 
in advance. In this position the movement of the interior 
substance is seen to advantage. In the large swarm-ceJls of 
Amaurochcete atra it may almost be described as streaming, the 
granules passing from one end to the other in constant flow; 
the hyaloplasmic extension at the posterior end continually 
changes its form and often detaches portions which cannot 
Fig. 1.— Didymium diffokme Duby. 
a. Spore. 
h. Swtarm-cell escapinp; from the spore-case. 
c. Newly Latched swarm-cell containing a 
nucleus and three vacuoles. 
d. Flagellated swarm-cell. 
e. Swarm-cell, with two vacuoles containing 
bacteria, and produced at the posterior 
end into pseudopodia, to one of which a 
bacterium is attached. 
/. Amoeboid swarm-cell. 
Magnified 720 times. 
