Fig. 156 Bacillariophyceae. A, Melosira granular a (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 genera- 

 tions are shaded appropriately, en = central nodule, /= foramen, 

 ^= girdle, /z =hypotheca, p«= polar nodule, r= raphe, «;= valve, 

 w =wall of valve. (A, H, after Smith; B-G, after Fritsch.) 



a plain area in between (pseudoraphe) or else a slit that varies in 

 form and structure (raphe). In the Centricae these structures are 

 absent and the striae are arranged radially. The raphe is connected 

 with movement, as only those forms possessing one have the power 

 of locomotion, and although the mechanism is not completely 

 understood it would seem to be connected with friction caused by 

 the streaming of protoplasm. Streams of mucilage pass from the 

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



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