120 BACILLARIOPHYCEAE (DIATOMACEAE) 



of locomotion, and although the mechanism is not completely 

 understood it would seem to be connected with friction caused by 



Fig. 84. Bacillariophyceae. A, Melosira granulata (Centricae) ( x 624). B, 

 Pinnularia viridis (Pennatae), girdle view. C, same, valve view. D, P. viridis, 

 union of valve and parts of adjacent girdle bands. E, P. viridis, termination of the 

 two parts of the raphe in the polar nodule. F, P. viridis, diagrammatic view 

 showing the two raphes. G, movement of P. viridis as shown by sepia particles. 

 I, in valve view; 2, in girdle view. H, diagram to illustrate successive diminution 

 in size of plant. The half-walls of the different generations are shaded appro- 

 priately. cw = central nodule, /= foramen, ^ = girdle, /? = hypotheca, ^n = polar 

 nodule, ?- = raphe, z; = valve, z:; = wall of valve. (A, H, after Smith; B-G, after 

 Fritsch.) 



the streaming of protoplasm. Streams of mucilage pass from the 

 anterior polar nodule down to the centre of the plant body where it 

 masses and then spreads out posteriorly in the form of a fine thread 

 (fig. 84 G). Each cell is surrounded by a cytoplasmic fining with a 



