68 THE AMERICAN MONTHLY [Mar 
hundreds and many thousands, tied. together. Being so — 
numerous and laid in different days, embryos of different 
erades of development may be had for observing the cir- 
culation of the blood. The eye catches at a glance a beau- 
tiful sight of the whole circulatory system, and follows 
_with delighted attention, the streams of blood starting 
from the heart, running in the arteries and veins, and re- 
turning to the heart, whose beatings are conspicuously 
seen. The elongated globules of the fish’s blood are dis- 
tinctly seen, forming inside the blood vessels something 
like a string of beans. Ff. J. Medina, Corinto, Nicaragua, 
Central America. 
STEREO-MICRO-PHOTOGRAPHY.—More than forty years 
ago I made many experiments as to the best means of 
obtaining stereoscopic photographs of microscopic ob- 
jects. Results with the use of binocular microscopes 
were unsatisfactory, as all adaptations of prisms _pro- 
hibited the employment of the higher power objectives, 
because only half the diameter of the lenses could be 
used, and this objection exists in a greater degree with 
the Riddell binocular shown in the article (erroneously 
termed the Stevenson). I obtained the best results with- 
out any prisms whatever, and could employ the very 
highest powers by getting rid of such impediments. 
The method was very simple. A small segment of the 
circle from the object-glass was stopped off by a black 
card, and a photo taken of a diatom or other objects. 
Next another impression was obtained on a separate 
plate, with an opposite and similar segment of the circle 
of the field stopped off. The resulting pair of pictures 
to be viewed with a sterescope. : 
But as diatoms and Lepidoptera scales are very thin 
and mounted flat, it is desirable in order to get a raised 
effect to enhance or exaggerate the perspective; there- 
fore, for each exposure the object may be set a little out 
