1897J MICROSCOPICAL JOURNAL. 181 



Remarks upon the Diatomaceae. 



By J. G. WALLKK, 



LONDON. 



[Fioiu the President's Address before The Quekett CI ah. J 



They are Lil)i(;[uitous, and found every wliere in water, 

 whetlter in tlie ocean, or river, or tiie merest triciiling 

 rill. lti« an interesting- fact, you can in many instances 

 predict the cliaracter of what you will find, according to 

 the conditions under which they exist, and they have 

 more than any other org-anism been favored by constant 

 research. Tue development of the microscope itself has 

 gone on coincidently with our knowledge. Some diatoms 

 have long been test objects wherewith to examine the 

 highest powers. At the time when Ehrenberg wrote, 

 probably most observers considered with him that they 

 belonged to the animal kingdom ; and this view lingered 

 on, finding its supporters even when Andrew Prichard, 

 in 1801, j)ublislied his admirable compilation on the 

 "Infusoria." Although this is now quite given up, one 

 must not condemn too readily views that were partly 

 suggested by the movements of certain species. Truth 

 is a growth, the result of observation, but it is slow in 

 progress, as the history of opinion on the most important 

 of subjects declares unto us. But, if we assume that the 

 movement of the Naviculacea' was due to animal nature, 

 the next step was to tell us how this was accomplished. 

 So some observers distinctly saw a ciliated a[)paratus. 

 This, however is the old story ; you can always see what 

 you wish to see, that which your mind has determined ; 

 and it is not agreeable to many, perhaps to most minds, 

 to think that your eyes may deceive you. Yet this is a 

 lesson that the microscopist must learn, and it is an 

 important one. The study of the Diatomaceae continu- 

 ally imposes this upon us. One species has exercised all 



