X.] PROTOCOCCUS. 391 



The multiplication of Protococcus takes place by means of 

 actively locomotive spores, termed zoospores. These are of 

 two kinds. The larger, or macrozoospores, are produced by 

 the division of the contents of one of the ordinary cells into 

 two or four portions. These portions assume a pear-like 

 shape and become free by the resorption of the wall of the 

 mother- cell. When they first escape the zoospores are 

 naked protoplasmic bodies (primordial cells) destitute of any 

 cell-wall. They swim actively through the water by means 

 of two delicate processes of the protoplasm, termed cilia t 

 which are inserted at the pointed end of the zoospore. The 

 movement is of a double kind, the progressive motion, in 

 which the pointed ciliated end goes foremost, being accom- 

 panied by a rotation of the zoospore about its long axis. 

 The macrozoospore soon acquires a thin cell-wall, through 

 which the cilia protrude. The wall does not remain in 

 immediate contact with the protoplasm of the primordial 

 cell, but becomes separated from it by a space containing 

 clear cell-sap. This space is however traversed by fine 

 radiating protoplasmic threads. The internal structure is 

 similar to that of the vegetative cell, each zoospore contain- 

 ing a nucleus and chromatophores. The ciliated end con- 

 sists of colourless protoplasm only. 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, and arrest their movements. 



The smaller, or microzoospores, are produced by the division 

 of the vegetative mother-cell into a larger number of por- 

 tions, the number being always some power of two. They 

 differ from the macrozoospores, apart from their size, in 

 never acquiring a cell-wall so long as their movement con- 

 tinues. In other respects the two kinds of zoospores agree. 



