274 Transactions of the Boydl Microscopical Society. 
II. — Note on the Markings of Frustulia Saxonica. 
By Assistant-Surgeon J. J. Woodward, U. S. Army. 
{Bead hefore the Eoyal Microscopical Society, November 3, 1875.) 
Plates CXXIV. and CXXV. 
On returning from my last summer's vacation my attention was 
directed a few days ago, for the first time, to a letter by Mr. W. J. 
Hickie in the July number of the ' Monthly Microscopical Journal ' 
(p. 32), on the subject of the markings of Frustulia Saxonica, 
which seems to call for some comments from me. 
Mr. Hickie refers to a paragraph in the * Monthly Micro- 
scopical Journal ' (vol. ix., p. 86) headed " Frustulia Saxonica as a 
Definition Test," which he, however, thinks may possibly misrepre- 
sent my views, and remarks — " What is there said is by no means 
very clear ; but it certainly does make him assert one of two 
things : either (1) that Frustulia Saxonica is a one-lined object 
(i. e. has transverse, but no longitudinal lines) ; or (2) that, 
though it undoubtedly has transverse, and may possibly have 
longitudinal lines as well, no one as yet has succeeded in seeing 
the latter, but that those who fancied they saw them, as Dippel 
and others, have been deceived by ' difiraction phenomena.' " I will 
frankly say that the second of these views very fairly represents 
my opinions on this subject, although it is not precisely what I 
said. 
The paragraph quoted by Mr. Hickie is abridged from a " Note 
on the Frustulia Saxonica as a Test of High-Power Definition," 
which I published in the ' Lens' for October, 1872 (p. 233), and 
of which I send herewith two copies, with the request that one of 
them may be forwarded to Mr. Hickie. The original article was 
illustrated by a Woodburytype plate, of which I have now no 
spare copies ; I send, however, two silver prints (marked A) from 
the negative used in its preparation. In this " Note " I quoted 
Dippel's description,* which attributes to Frustulia Saxonica both 
longitudinal and transverse striae, and estimates the first at 18 to 
20, the second at 34 to 35 in the one hundredth of a millimeter. 
I stated that I myself found the transverse striae count 85 to 90 in 
the one thousandth of an inch, which agrees substantially with 
Dippel's figures, but said, " The longitudinal striae of Dippel, how- 
ever, I must regard as diffraction phenomena," and went on to 
assert that as I observed them "they varied too much in their 
distance apart, with varying obliquity of illumination, to bear any 
other interpretation." It will be observed that I did not, in my 
* From ' Das Mikroskop und seine AnwenJung.' Erster Theil. Braunschweig, 
18G7. 8. 132. 
