PROTOZOA 23 
simple fission. Many Flagellata form colonies, the individuals 
of which are imbedded in a gelatinous matrix. 
Luglena viridis (Fig. 17) is a minute oval Flagellate found in 
puddles by the wayside, or on roofs, ete. It has a thin cuticle, 
and undergoes curious rhythmical changes of outline. The elon- 
gated spindle-shaped body shortens, and becomes correspond- 
ingly thicker. The thickening appears then to travel to the 
posterior end of the body and die out. The animal has at this 
moment its elongated spindle-shaped form; it then shortens 
again, and the whole movement is repeated. At the anterior 
end is a single long flagellum, which by its lashing drags 
the body swiftly through the water. Lankester has dwelt 
on the difference between the action of such a flagellum 
(tractellum) and of one that propels an organism in front 
of it, as the tail of a spermatozoa or the flagellum of Bacteria 
(pulsellum). 
tound the base of the flagellum is a depression, the mouth, 
which leads into the central protoplasm; and close to this, and 
apparently opening into it, is a reservoir communicating with a 
contractile vacuole. A pigment spot also is found in the same 
region, but the reticulate nucleus occupies the centre of the 
body. The whole body is coloured green, by chlorophyll 
granules. Grains of paramylum, a body with the same com- 
position as starch, are also found in the protoplasm. 
Hypnocysts, or resting encysted forms, are frequently formed 
amongst the Flagellata, when they find themselves in un- 
favourable circumstances. The encysted Huglena may emerge 
after a certain period of rest from the Hypnocyst, or it may 
whilst in the cyst divide into 2 or 4 spores each of which 
emerges as a young Euglena. Reproduction by multiple fission 
has also been described in this species, a vast number of spores 
being formed, each of which grows into a new individual. Con- 
Jugation also takes place in the Flagellata, and is usually 
followed by encystment and the division of the contents of the 
cyst (sporocyst). At other times fission may occur in the free 
state. Sometimes macrogonidia and microgonidia are produced, 
and the latter fuse with one another or with adult individuals 
(Protococcus). 
The Flagellata are divided into two groups: the JLzsso- 
