II.] PROTOCOCCUS. 13 



points, where it protrudes through the wall in the form of 

 long vibratile filaments or cilia, and by the lashing of these 

 cilia 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 invisi- 

 ble 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 

 Alga, to which Protococcus belongs, give rise, under certain 

 circumstances, to locomotive bodies propelled by cilia, like 

 the locomotive 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 else- 

 where, is thus readily accounted for by the transport of the 

 dry Protococci by winds. 



