144 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
with a “ Low” pneumatic shutter, this model being chosen on account 
of the small amount of space it occupies, allowing it to be introduced 
between the camera and the microscope. This was accomplished by 
clamping the shutter to the collar on the front-board of the camera, 
another similar collar being screwed to the front of the shutter for the 
light tight connection with the microscope. With the microscope in the 
horizontal position the light was taken directly from the mirror of 
the heliostat and diffused by means of a disk of blue ground-glass 
placed in the substage immediately behind the iris diaphragm, and then 
passes through a simple condensing lens to the object on the stage of 
the mieroscope. The immediate source of the light, the ground-glass, 
is thus brought near to the object to be photographed, giving a brilliant 
illumination and permitting the use of a small diaphragm. 
The most difficult task was to confine the animals to be photographed, 
more particularly with the microscope in the horizontal position. The 
device which proved most serviceable for flat or discoidal objects was a 
parallel compressor of the model of Hermann Fol Rings were cut 
from pure rubber tissue of different thicknesses, the ring to be em- 
ployed for amy particular object being a little thicker than the object 
itself. The rubber ring was then placed on the lower plate of the com- 
pressor and pressed into contact with it by means of the finger. The 
object is then brought into the centre of the ring, and water added with 
a pipette until the inside of the ring is completely filled, and the upper 
part of the compresser carefully screwed down until it comes in contact 
with the rubber, the superfluous water being at the same time squeezed 
out. If this be done with care, the inside of the ring will be com- 
pletely filled with water and contain no air bubbles. There should be 
just enough pressure to allow the upper glass of the compressor to come. 
in contact with the object. This can be determined by holding the com- 
pressor vertically, and screwing down the upper plate until the objeot 
ceases to sink. The compressor can now be clamped to the stage of the 
microscope in any position. By employing rubber rings of sufficient thick- 
ness, aquaria can be contrived in this way one eighth of an inch in depth. 
In photographing the rounder and plumper forms, amy pressure upon 
tho animal would produce a sensible change in shape. Such forms, 
therefore, were placed in small deep watch glasses and confined by 
glass rings, the microscope being placed in a vertical position, the camera 
however remaining horizontal. The connection between the microscope 
and camera was effected by means of the prism end of an Oberhäuser's 
camera lucida, to which the light tight collar had been adjusted by 
