THE PRESIDENT'S ADDRESS. 337 



than of the hideous scenes that once took place at the corner of 

 Edgware Road, in microscopic beauty at its source, and the 

 associations at its outpour. 



But when we speak of Diatomaceae, we cannot do otherwise 

 than remember the part they play in microscopical history. 

 They are ubiquitous, found everywhere in water, whether in the 

 ocean, or river, or the merest trickling rill. It is an interesting 

 fact, that you can, in many instances, predicate the character of 

 what you will find, according to the conditions under which they 

 exist, and they have more than any other organism been favoured 

 by constant research. The 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 1861, published his admirable com- 

 pilation 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 assumed that the movement of the Navi- 

 culaceee was due to animal nature, the next step was to tell us 

 how this was accomplished. So some observers distinctly saw 

 a ciliated apparatus. 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 continually imposes this 

 upon us. One species has especially exercised all the faculties 

 required in minute examination — the Pleurosigma angulatum 

 — which has in itself a history singular in the various waves of 

 opinion and attempted demonstration. The markings of its 

 silicious envelope at first presented stria?, which further magni- 

 fication determined into a series of semi-circular bosses, or at 

 other times, according to other views, so many depressions or 

 apertures. The first was once attempted to be illustrated by 

 a glass tumbler, the sides of which consisted of so many raised 

 Journ. Q. M. C, Series II., No. 40. 24 



