i ;o 



STRUCTURE OF DIATOMS 



chains, while others are imbedded in a gelatinous mass of a 

 more or less regular form (Fig. 94, D). The cells are covered 

 by two valves, one of which overlaps the other like the cover 

 of a box. Therefore a diatom presents two quite distinct ap- 



Fig. 95. Fig. 96. 



Fig. 95. Plankton forms of diatoms: A, Coscinodiscus, B, Planktoniella. 

 Below seen from side. — After Gran. 



Fig. 96. Structure of the diatom, Pinnularia: A, valve view. B, girdle 

 view. C, cross-section, the two dark hands showing the position of the 

 chromoplasts in the diatom — />, pore in wall which appears as a line in A, 

 running from the ends towards the center of the valve. — After Lauterborn. 



pearances — the top or valve view and the side or girdle view 

 ( Figs. 96, 97). This difference is further intensified by the 

 sculpturing of fine lines that appear upon the walls. An inter- 

 esting feature about these valves is the fact that thev are com- 



