CYANOPHYCE^E. 



219 



288. The genera Protococcus, C'hlorococcum, and one or 

 two others, are probably to be placed nc ar the Palmellaceae, 

 although their autonomy is doubtful also. They are all 

 unicellular in the strictest sense of the term, and reproduce 

 mainly by fission. In their resting stage they are spheroidal ; 

 in their motile stage they are provided with two cilia. The 

 latter form is said to arise from the former by internal cell- 

 division, which results in the production of "gonidia"of 

 two sizes, the larger being termed macrogonidia, and the 

 smaller microgonidia. 



These organisms are common in shallow pools, in the gut- 

 ters of roofs, and on the wet earth. 



(a) On account of their ready perishability, Protophytes are scarcely 

 found in a fossil state. Sckiinper records a species of Nostoc from the 

 Tertiary. 



(6) The relationship of the classes of the Protophytes may be indi- 

 cated by the following diagram : 



ARRANGEMENT OF THE CLASSES OF PROTOPHYTA. 



Cyanophycese. 



Myxomycetes. 



Schizomycetes. 



