A.TOMACEJ:. 423 



The accompanying illustra. 

 tion is drawn from, a photo- 

 graph of Frustulia Saxonica, 

 one of the most difficult of the 

 " Probe Platte," Moller's bal- 

 sam-mounted diatoms, resolved 

 by a Tolles' ^ duplex front 

 immersion objective. The lon- 

 gitudinal lines as well as the 

 transverse are well seen over 

 the greater .part of the frustule. 

 The measurement of the trans- 

 verse lines given by Mr. Wells, 

 is 88,'001 inch. Professor Mor- 

 ley puts them at 81'5 to 82,'001 

 inch. The midrib and margin 

 of the diatom are quite thick, 

 and, consequently, when very 

 oblique light is used, they pro- 

 duce diffraction phenomena, 

 and which, in some instances, 

 obliterate the whole of the 

 markings. The f rust ale, how- 

 ever, in this instance is mount- 

 ed in balsam, and the lines are 

 therefore fainter than they 

 would be if mounted dry. The 

 kind of illumination employed 

 by the photographer was Wen- 

 ham's reflex illuminator. The 

 beaded appearance of the sur- 

 face is much better seen in the 

 photograph than in the wood- 

 cut. 1 



Movements of Diatoms. The 

 researches of Professor Max 

 Schultze, of Bonn, published 

 1865, appear to throw some 

 light on the vexed question 

 of the movements of the 



Frustulia Saxonica (x 1,800 di- (1) The English Mechanic, July 23, 1880. 



ameters) from Moller's balsamed 



Probe-Platte. From a photograph by Mr. S. Wells, of Boston, U.S.A. 



