PROTOZOA 23 



simple fission. Many Flagellata form colonies, the individuals 

 of which are imbedded in a gelatinous matrix. 



EugUna viridis (Fig. 17) is a minute oval Flagellate found in 

 puddles by the wayside, or on roofs, etc. 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). 



Eound 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 Eioglena may emerge 

 after a certain period of rest from the Hypnoeyst, or it may 

 whilst in the cyst divide into 2 or 4 spores each of which 

 emerges as a young Euglena. Eeproduction 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 

 (Frotococciis). 



The Flagellata are divided into two groups : the Idsso- 



