444 MICROSCOPY. 
that only one slide in twenty, perhaps one scale in five thousand, : 
was of any use. In his slide prepared by Mr. R. Beck there are 
only two well marked scales, which appear to be the exception and 
not the rule. Dr. Josiah Curtis, of Knoxville, Tenn., has been 
successful in collecting species of Lepisma, ‘‘Podura,” ete. 
Tur Srupy or “ Dirricutt” Draroms.— Mr. J. Edwards Smith 
of Ashtabula, Ohio, writes the following note which is suggestive 
of the experience of many microscopists who study the finer dia- 
toms without making a specialty of them. 
“I find that Pritchard describes Navicula cuspidata as having 
close transverse striz. I have slides of this diatom, mounted dry 
„and in balsam, and with my Tolles’ 4 dry, or 45 wet, have no diffi- 
culty in showing longitudinal striæ, far finer than the transverse; 
indeed when mounted dry both sets can be plainly seen at once. 
Is there anything remarkable about this? 
I notice that Möller places Navicula crassenervis as the 18th on 
his ‘Probe Platte’. I fail to discover striæ on this diatom either 
in balsam or mounted dry. Pritchard says they are sometimes 
wanting. The objectives above named show the fine lines in No. 
17 (Cymatopleur elliptica) very nicely, but fail on Nos. 18, 1 
and 20. Our friends here are interested to know what others are 
doing with this ‘Probe Platte.’ Has Amphipleura pellucida been 
resolved in balsam? When, by whom, and with what lenses?” 
Ans.—Nothing can be more certain than the uncertainty of what 
has been known, in regard to the markings and structure of diae 
toms. It would be rash at present to pronounce any shell as! 
from markings, and would probably be repeating a mee o 
often made already. Different shells of the same spea i 
eis necess®y 
greatly in “difficulty,” but no explanation or excus wie 
for a dry } failing to go entirely through the series on ps io 
plate. It is by no means easy, though sometimes pit 
resolve A. pellucida in balsam with dry lenses and ordinary! m - 
nation. With immersion lenses, however, and na 
illumination, there is no difficulty in accomplishing this with wn 
tives of Tolles, Wales, Powell and Lealand, Beck, mar . 
Nachet, and doubtless several other makers. About two cil - 
ago Count F. Castracane resolved and photographed A. 7 For & 
in balsam, with French lenses and monochromati¢ sunligh H i 
a method by which this can be easily accomplished seë == 
ward’s paper in the NaruraLisr for April last. 
