338 N. E. BROWN ON THE STRUCTURE OF DIATOMS. 



Fig. 1 1 . Fragment of the shell of Xitzschia scalar is, showing 

 pores, x 3,000. Styrax mount, central light, green screen. 



Fig. 12. Fragment of the grating of Amphipleura Lindheimeri, 

 X 3,000. Styrax mount, central light, green screen. 



Fig. 13. Fragment of the shell of a small species of Pinnularia 

 from the Cherryfielcl deposit, x 3,000, showing what are believed 

 to be a row of pores down the centre of the outer wall of each 

 cavity. Picric-piperine mount, central light and green screen ; 

 can also be seen with dark-ground illumination without a funnel- 

 stop in the lens and no green screen. 



Fig. 14. Fragment of the grating of Stauroneis ])hoenicenteron, 

 x 3,000. Picric-piperine mount, oblique illumination by Leitz 

 dark-ground illuminator. 



Fig. 15. View of one of the hexagonal cavities of the valve of 

 Triceratiam favus as seen from the outside of the diatom, showing 

 the membrane which closes it on the outer side, x 1,500. Styrax 

 mount ; outline drawn with a camera-lucida as seen under a 

 monocular, shading added as seen under a binocular with oblique 

 illumination. 



Fig. 16. View of one of the hexagonal cavities of the valve of 

 Triceratium javus as seen from the interior of the diatom, showing 

 the raised appearance of the membrane, x 1,500. Styrax mount, 

 drawn in the same manner as fig. 15. 



Fig. 17. Fragment of the membrane shown in fig. 16, drawn as 

 seen at a magnification of 3,000 diameters, but enlarged to about 

 10,000 diameters, to show the pit-like nature of the dots upon 

 the membrane. 



Joi'.m. Qucl-ett Microscopical Club. Scr. 2, Vol. XII. No. 74, April 1914. 



