ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
415 
In bis experiments the author used a large Reichert Microscope. 
In this instrument on the upper end of the body-tube a ring (fig. 43) 
is screwed. In this is fitted a tube which carries the eye-piece and 
can be introduced and removed at will. For use with the auxiliary 
apparatus the ring is made to slide into instead of being screwed 
on the body-tube (fig. 44). It can thus be easily removed together 
with the tube carrying the eye-piece, and replaced by a longer tube 
containing at the lower end a condensing lens, and at the upper 
the auxiliary Microscope which is adjustable by rack and pinion 
(fig. 45). 
1 he complete apparatus is represented in fig. 46. 
It is not intended to make use of these very strong magnifications 
for continuous work, but only for the closer examination of details 
left in doubt by the ordinary method of observation. For such pur- 
poses the diminution of the field of view is no disadvantage. 
As source of light the author uses the Koch-Wolz Microscope 
lamp combined with the Auer incandescent light, and also the electric 
incandescent light. The last allows of a magnification of from 8000 to 
10,000 times. 
The author has applied his method of observation in order to decide 
the vexed question of the shape of the pearls of Pleurosigma ancjulalum. 
With a Reichert homogeneous-immersion 1/20 and strong eye-piece 
No. V. the pearls give their usual hexagonal appearance, but by the 
use of the auxiliary Microscope with objective No. 2 and eye-piece 
I. or II., they are seen to be unmistakably rhombic in outline. The 
upper surface is curved and the edges and corners are truncated. The 
acute angles of the rhomb are rounded, so that on account of the 
deeper shadow, under lower magnification they give the appearance of 
two parallel sides of the hexagon. In some parts of the valve the 
pearls had disappeared, leaving however the very fine membrane on 
which they rested. This membrane was found to have kept the im- 
pression of the pearls as a rhombic pattern. 
Surirella gemma was also examined. The striations are composed 
of small particles which give rise to the so-called “ basket-like net- 
work.” Each row appears like a string of pearls.* Here again in many 
cases pearls have disappeared, leaving a membrane marked by very fine 
striations. In the perfect specimen this striation does not coincide with, 
but is covered by the lines of the “ basket-like network.” With ex- 
tremely high magnification, however, and by careful adjustment, it is 
possible to see first the network and then the striation. The combined 
images give the false appearance of elongated hexagons. 
Zentmayer’s Dissecting Microscope.f — This instrument, made pri- 
marily for botanical work, has a circular base 5 in. in diameter, and is 
made of polished brass. A stout pillar rises about 6 in. on one side, 
to which a broad stage (4 in. by 5) and a jointed arm for carrying the 
lenses are attached. A plane mirror is adjusted to the base beneath 
the stage. The latter carries spring clips, which are easily removed to 
* See this Journal, 1890, Plate II. 
t Amer. Mon. Mier. Journ., xiii. (1892) p. 2. 
