II-] PROTOCOCCUS. 15 



h. Cells multiplying hy fission : 



a. Simple fission. The protoplasm divides into 

 two segments and then forms a partition 

 dividing the sac; the halves either separate 

 at once, and each rounds itself off and becomes 

 an independent cell; or one or both halves 

 again divide, in a similar way, before they 

 separate, and so three or four new cells are 

 produced. 



/3. Cells multiplying by budding, like Torula; rare. 



b. Motile stage. 



a. Mount a drop of water containing motile Proto- 

 coccus, and examine with a high power. Note 

 the minute, actively locomotive green bodies, of 

 which two varieties can be distinguished, 



a. Small, green, pear-shaped cells. 



Run in iodine, which stains them and also 

 kills them and stops their movements : note 

 then the absence of any distinct sac, and the ■ 

 two cilia attached to the narrower end. 



/3. A form larger than the last and apparently 

 intermediate to it and the still cells. 



Kill and stain with iodine as before. Note 

 the central granular coloured (protoplasmic) 

 portion — the loosely enveloping unstained sac 

 — the two cilia prolonged from the protoplasm 

 through an opening in the sac. 



c. Try to find specimens in which the movements are 



becoming sluggish, and see the cilia in motion. 



