SELECTION, ETC., OF OBJECTS FOR PHOTOGRAPHING. 99 
protoplasm of the former arrests light entirely, 
and we have in a positive print only a uniformly 
black mass with circular outline, surrounded by 
another line representing the cell wall, to repre- 
sent the beautiful little ruby sphere with its more 
or less granular contents. The green color of 
P. viidis is better adapted for photography. 
Plate II. Fig. 1, represents one stage in the life 
history of the last-named species. 
The unicellular Algse are found in pond and 
ditch water, upon the surface of moist mud, damp 
walls and stones, etc. They are interesting micro- 
scopic objects, and suitable for photographing. 
P. nmvalis grows upon the surface of the snow in 
high latitudes, and upon snow-clad peaks in more 
temperate regions. An amplification of from two 
to six hundred diameters will be required. For 
the lower power, Tolles’s four-tenths-inch or 
Powell & Lealand’s one - half-inch objective may 
be used; for the higher, a good one-fifth-inch 
lens. 
INFUSORIA. 
Many of the Infusoria may be successfully pho- 
tographed, but it will be necessary to exercise 
great care in the preparation of slides for this 
purpose. Generally, but a single individual should 
be in the field of view, and this should be a perfect 
specimen; for it is difficult to obtain fields con- 
taining several individuals all in the same plane, 
and in order to show cilia, flagella, and interior 
details of structure, high powers and very careful 
focusing will be required. 
