The microscope and its revelations . to be identical with those of tneRichmond earth.—Nearly aUied to the preceding is tliebeautiful genus Actinocyclus (Eig. 84), of which also the frustules are discoi-FiG, 84. dal in form, but of which each valve,instead of being flat,has an undulatingsurface, as is seen infront view (b) ; giv-ing to the side view(a) the appearanceof being markedby radiating to this pecu-liarity of shape, thewhole surface can-not be brought into focus at once, except with a Jow power;and the difference of aspect which the different radial divisionspresent in Eig.
The microscope and its revelations . to be identical with those of tneRichmond earth.—Nearly aUied to the preceding is tliebeautiful genus Actinocyclus (Eig. 84), of which also the frustules are discoi-FiG, 84. dal in form, but of which each valve,instead of being flat,has an undulatingsurface, as is seen infront view (b) ; giv-ing to the side view(a) the appearanceof being markedby radiating to this pecu-liarity of shape, thewhole surface can-not be brought into focus at once, except with a Jow power;and the difference of aspect which the different radial divisionspresent in Eig. 84, is simply due to tlie fact, that one set isout of focus, whilst the other is in it, since the appearances arereversed by merely altering the focal adjustment. The number ofradial divisions has been considered a character of sufficient im-portance to serve for the distinction of species; but this is pro-bably subject to variation; since we not unfrequently meet withdisks, of which one has (say) 8 and another 10 such divisions,.
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Keywords: ., bookcentury1800, booksubjectmicroscopes, booksubjectmicroscopy
