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3 Sot OMS a Dae 
310 MICROSCOPY. 
an excuse for them. So many competent microscopists have — 
written upon this subject that the writer would fain be silent were _ 
it not for a firm belief in the superiority of the instrument he — 
used, for this kind of investigation. In fact this excellent glass — 
gives advanced work on almost every test tried, and fully justifies : 
‘the confidence reposed in it. The observations recorded below, — 
unless where otherwise stated, were made with a Tolles ṣẹ im- — 
mersion objective of 165° angle of aperture, and generally a — 
Tolles’ two inch eye-piece, giving an amplification of 2500 diame- — 
ters. A 
Eupodiscus Argus.— My attention was especially called to this — 
shell by having noticed the wide difference between the views of z 
Mr. Henry J. Slack, Mr. Samuel Wells and Mr. Charles Stodder. — 
My observations are corroborative of the idea of two plates as e 
asserted by Messrs. Stodder and Wells. Using a 3 objective with — 
power of 340 times obtained by high eye-piece and extending — 
draw tube, and using a Lieberkiihn, the outside or coarser mark- 
ings on specimens mounted convex side uppermost are white with © | 
white cloud illumination. An erased space on one shell and the 4 
holes or depressions through which Slack’s four large ‘ spherules” i 
are seen are now black. They, then, are not covered by the ex- 
ternal ‘‘ crust.” 
The slide was then turned over and the inside of the same 
specimen examined by the same method, and on the more favor- 
able portions of it the finer net-work of the inner plate is also sap ee 
in white, the ‘‘spherules” being perfectly black. By this resect 
light the “four spherules” are plainly seen to be dark openings — 
in the white plate and the’ net-work is clearly traced across the : 
areolæ in the outside plate. The diatom looks like a piece of : 
coarse white netting laid over a finer piece. ; 
Under the Tolles 1, and with transmitted light, whether ¢? 
tral or oblique, it matters not, all portions of the surface of both 
the upper and the lower plates are found to be covered with, 0 
‘composed of, a still finer net-work with irregular oval meshes like 
the two coarser ones. pe 
The place in the shell above referred to, where the layers are 
erased, denuding an interior structureless “vail,” gives an OPE 
tunity to observe the edges of the fractured layers. The broke 
edges of both plates bordering on the erasure show the jagging 
this finest net structure. The arrangement of the finest are? 
