1887.) MICROSCOPICAL JOURNAL. 105 
I have thus far attempted, with as little digression as possible, to point out 
all the features of the section in the field when the microscope is pointed at 
the wall of the alveolus marked F (fig. 3). With so many details, each one 
of which must be noted and weighed carefully before any judgment can be 
formed, what wonder that the beginner in histology fails to see the point elo- 
quently enlarged upon in a diagrammatic sketch! But any one who will 
carefully follow some such mode of study a few times will soon begin to 
acquire the power of almost instantaneously seeing and interpreting all these 
appearances, to form a conception of the actual structure of the sections 
under observation. Having thus noted the points to be observed, and what 
is actually seen, let us take the further higher step of the histologist. the care- 
ful judgment from the appearances to the facts of structure, or, in the biolo- 
gist’s parlance, the ‘interpretation of the section.’ We have already 
anticipated this step to some extent. In the actual study of a skilled histolo- 
gist the two processes are practically simultaneous, not successive, as here 
necessarily set forth. 
Resolution of pearls of Amphipleura. 
By ROMYN HITCHCOCK. 
Dr. Van Heurck has sent some very good and interesting photographs to 
. the writer, showing the excellence of his method of work and the extremely 
fine results it has afforded him. Among these the most striking, as well as — 
the most difficult test, is the resolution of the Amphipleura pellucida into 
beads or pearls, which, in the photograph, are distinct, and far more satis- 
factorily shown than in another print received a year ago. 
The method employed was first described in full in these columns,* and 
need not, therefore, receive further attention at this time. The photographs 
received are the following :— 
1. Pleurasigma angulatum,\W.Sm. The specimen was mounted in the 
yellow medium. The photograph shows very clearly that the valve is made 
up of several layers—certainly of two, which are distinctly seen. Near the 
raphe the upper or superior layer is broken and portions of it have been 
removed, showing the inferior layer with its alveoles corresponding to the 
markings of the upper layer. 
Valves in this condition are not uncommon, and these observations can be 
readily verified. 
2. Surtrella gemma, Ehr. Photographed from a mount in the yellow 
medium with an initial magnification of 600 diameters and enlarged to 3000. 
An excellent demonstration of the fine definition of the Zeiss 3 mm. lens. 
We have always regarded this diatom a very trying test. 
3. Amphipleura pellucida. Resolution of the transverse striz. 
4. The same. Resolution of the longitudinal striz. 
5. The same. Resolution of the pearls. 
The last three are from the same valve, taken with a direct magnification 
of 1100 diameters, using a Zeiss objective of 3 mm., combined with a cor- 
recting ocular of 25 mm., by the same maker. The Wenham reflex illu- 
minator was used and monochromatic sunlight. The longitudinal lines have 
never before been photographed, and the pearly or beaded structure has never 
before been seen by transmitted light. 
A careful examination of the prints will convince any skeptic that there is 
no illusion about the resolutions. Dr. Van Heurck informs us that Profes- 
* February, 1885. 
