DIATOM MOTION. T4I 



A Study of the diagrams and their accompanying data 

 seems to show : — 



Firstly, That the localized area, illuminated by the par- 

 ticular quality of light that is given by a Welsbach mantle, 

 has no noticeable attraction for the species of Navicula, Cyni- 

 hclla, Staurfl)icis and N^ifzscliia used in these experiments. 



Secondly, A veiyinefficient illumination — an illumina- 

 tion, especially in the second series, quite too feeble to operate 

 with any vigor on the chlorophyll — was no bar to continued 

 motile activity, at least in the case of these particular species, 

 and for the length of time the observations continued. 



Note. — These ol^servations were made with an aniplificalion of 70 

 diameters. The original diagrams having lieen drawn to scale, it 

 becomes possible to deduce the rate of motion 1))' measurements of 

 straight portions of the paths between timed points, as follows : — 



Navicula gi})l)a Greatest observed speed, 0.557 imn- per minute. 



Van Heurckia rhomboides, " " " 0.782 " " " 



Nitzschia, species " " " 0.266 " " " 



Cymbella gastroides " " " 0.586 " " " 



Stauroneis Phoenicenteron, " " " 0.714 " " " 



These figures mean, approximately, that Van Heurckia traveled at 

 the rate of one and thirteen-sixteenth inches, and Nitzschia at the rate 

 of five-eighths of an inch, per hour. 



