II.] PROTOCOCCUS. 13 



the cell is propelled with a rolling motion through the water. 

 The movement of the cilia is so rapid, and their substance 

 is so transparent and delicate, that they are invisible until 

 they begin to move slowly, or are treated with reagents, such 

 as iodine, which colour them. 



Not unfrequently the cell-wall eventually vanishes, and the 

 naked protoplasm of the cell swims about, and may undergo 

 division and multiplication in this state. Sooner or later, the 

 locomotive form draws in its cilia, becomes globular, and, 

 throwing out a cellulose coat, returns to the resting state. 



For reasons similar to those which prove the vegetable 

 nature of Torula, Protococcus is a plant, although, in its 

 locomotive condition, it is curiously similar to the Monads 

 among the lowest forms of animal life. But it is now known 

 that many of the lower plants, especially in the group of Algcc, 

 to which Protococcus belongs, give rise, under certain circum- 

 stances, to locomotive bodies propelled by cilia, like the loco- 

 motive Protococcus, so that there is nothing anomalous in 

 the case of Protococcus. 



Like the yeast-plant, Protococcus retains its vitality "after 

 it has been dried. It has been preserved for as long as two 

 years in the dry condition, and at the end of that time has 

 resumed its full activity when placed in water. The wide 

 distribution of Protococcus on the tops of houses and 

 elsewhere, is thus readily accounted for by the transport of 

 the dry Protococci by winds. 



