184 Chlorophycece 



resemblance to the cells in Borzi's genus Hormotila, Each cell 

 contains a single chloroplast, sometimes distinctly parietal, but 

 frequently subcentral and filled with highly refractive oil-globules. 

 The presence of pyrenoids has not been definitely determined. 

 Multiplication takes place by division of the cells in two directions. 



Fig. 72. Polychcetophora lamellosa West & G. S. West, from Cirencester, 

 Gloucestershire ( x 370). 



P. lam.ellosa West & G. S. West is the only species of the genus and has 

 been found in Gloucestershire amongst Tolypothrix pygmoea. Diam. of cells 

 19 35/x; thickness of cell-wall 2'8 10'5^; length of bristles 86 183 /* 



(% 72). 



Family 2. VOLVOCACEJE. 



The plants contained in this family are either unicellular or 

 they consist of definite coenobia of cells. They are distinguished 

 from all other Protococcoideae by being ciliated and motile in their 

 vegetative condition. The coenobia consist of a definite group 

 of cells either united together by protoplasmic processes or super- 

 ficially arranged within the swollen wall of a mother-cell. The 

 number of cells in any ccenobium remains constant so long as the 

 individual exists, and they all arose by cell-division while the 

 plant was still an embryo within the wall of the original mother- 

 cell. 



The cells are rounded, angular, or ovoidal in form, generally 

 with a narrower anterior end to which are attached two, or rarely 

 four, cilia. The protoplasm of the anterior region of the cells is 



