114 Beck, on a Live-Trap and Parabolic Reflector, 
is required to keep these thin glass covers sufficiently in con- 
tact with, and yet free to move upon, the perforated plate ; 
this is effected by two light springs attached to a piece of 
brass (Figs. Ill and IV), which can be clamped at the end of 
the glass plate ; and these parts collectively, as in Fig. V, con- 
stitute the whole of the apparatus, but one or two points of 
detail require a little explanation. 
The piece of brass with the springs (Figs. Ill and IV) is 
clamped to the glass plate by first screwing down the larger 
milled head {h) until it just comes in contact with the glass, 
and then by screwing up the smaller milled head (i) against 
the under side of the larger one, which is thus pressed suffi- 
ciently upon the glass plate without any fear of breaking it, 
for it will plainly be seen that, as the resistance to the screw- 
ing down of the larger milled head alone is on one side only, 
the milled head, after once coming down upon the glass, would 
tilt with any extra screwing, and thus not only fail to hold, 
but also almost certainly break the plate. It is therefore 
necessary to understand the principle on which the two milled 
heads are used, or insecurity in clamping, and breakage, may 
prove sources of considerable inconvenience. 
Each perforated glass plate is provided at the opposite end 
to that where the springs are clamped, with a small boss {k) 
on either side, so that the slide may lie parallel with the stage 
of the microscope when placed upon it ; but as the plates are 
not all the same thickness, an " upper side is marked upon 
each, and this distinction must be observed when clamping on 
the springs. 
The thin covers (Fig. II) are each provided with a small 
brass boss (e), and when this is pushed under a corresponding 
hollow (/) on the under side of either spring they form a 
centre from which the cover may be turned either over the 
perforation in the glass plate or on one side of it. Any 
description as to the way in which a living object may be 
captured or afterwards fed and kept alive is so dependent 
upon the class of object under examination that my experi- 
ence is very limited ; I may, however, mention that a fine 
camel-hair pencil, slightly moistened, will hold, and seldom 
