182 THE AMERICAN MONTHLY [June 



the faculties required in minute (vvauiination — tiie Pleu- 

 rosio'ina an^ulatuin — which lias in it sc] fa. history singu- 

 lar in the various waves of ()i)inii)n and atten)i)ted dem- 

 onstration. The markings of its silieious envelo[)e at 

 first pr(^sent(Ml stria', which fui'ther magnih(-ation deter- 

 mined iuto a series of semi-circular bosses, or at other 

 times, accordinj-'- to other views, so many depressions or 

 apertures. Tlie first was once attempted to be illustra- 

 ted by a g-lass tumbler, the sides of which consisted of 

 so many raised bulbs. It was thought that a similar 

 material would be similarly atlected by the action of light 

 and thus would prove, or tend to prove, the true cou- 

 struction of the valve. In the theory of elevations, it is 

 not so long ago that arrangements were made in side 

 illuminations by a pencil of light, thus supposing to give 

 a true and artistic light anil sliade. Bu\, in both these 

 nice experiments, it seemed to be forgotten that they 

 were begun in a foregone conclusion : and, as I have 

 previously said, you naturally, in such a case, see what 

 you wish to see. Certain accidents, fractures, and pecu- 

 liarities inconsistent with the above-named views, assis- 

 ted by carel'ul illumination, seem now to have tolerably 

 settled the question to be on the side of apertures, and 

 my predecessor has worked successfully thereto. That 

 this must be the general consent on such markings 

 throughout the Diatomaceai must |)robablj^ be entertain- 

 ed, though it would be dangerous to atlirm that there 

 was no variation from it in the multiform changes of 

 nature. 



But the subject has btuMi so adniii-ably worked outand 

 recorded l)y two [lapers in our .loiirnal, one by Mi'. C. 

 Haughton ( iill, April, 18i>0, in which is well described 

 liis mode of [)reparation of the objects wherewith to 

 determine the st iiict uie. Another by Mr. Nelson, in 

 May, 1891, goes into llu> s;nne matter by the u.se of high 

 powers, and these papers, showing a working on differ- 



