LABORATORY EXAMINATION OF STOMACHS. 13 
beaker. The beaker is then held under a faucet, so that the rush of 
water will cause whatever insect remains may be present to float to 
the surface, where they 'can be decanted off with a filter of bolting 
cloth. The remaining matter in the beaker (generally seeds and fruit 
skin) is then collected on another filter, and from the two filters the 
material is transferred by means of a scalpel to separate smooth blot- 
ters about 3 inches square, and is ready for examination. Examina- 
tions are usually made with a dissecting microscope furnished with 
an achromatic triplet lens, but occasionally it is necessary to employ 
the higher powers of the compound microscope. 
The principal difficulty arises from the fact that birds often mutilate 
their food before swallowing it, and the gizzard afterwards reduces it 
to fine fragments. A song sparrow, for example, will seize a grass- 
hopper, pinch it a dozen times, pull off and eat the head, pull off the 
legs and wings and then swallow the abdomen, leaving the other 
parts. In the gizzard, with its powerful muscular walls, the reduc- 
tion of the insect is more complete, so that 
usually within two hours only a few bits of 
grasshopper dust remain. It is with such ma- 
terial that the examiner has most often to 
deal. But with practice his eye quickly detects 
amidst this dust a squarish, bicolored jaw with 
a grooved cutting-edge behind which is a 
grinder (see PL II, fig. 1). If the jaw is lacking, 
a little search seldom fails to reveal a tiny piece 
that looks like a human ear, but in reality is 
part of the knee-joint of the grasshopper (see 
PI II fi 0- 3^ ^ IG ' ~ — J aw °f May-beetle 
' J_> ' '" i top and side vie 
The remains of caterpillars found in bird stom- 
achs usually consist of the discolored broken skin, which has been 
twisted and rolled into compact little packets by the action of the stom- 
ach. Sometimes nothing is left by which to identify the insect except 
the concave jaws, the prominent spherical condyles of which, however, 
are unmistakable (see PI. II, fig. 8). Butterflies and moths may be dis- 
tinguished by the tiny tooth-scales of the wing (see PI. II, fig. 2) when 
the naked eye is unable to detect the presence of these insects. Beetles 
resist digestion more than caterpillars and grasshoppers, consequently 
pieces of their hard shells may be found in the stomachs for some time. 
These and other fragments serve to distinguish the different kinds. 
The hard parts of the genital organs of different species of May-beetles 
(see PI. II, fig. 4) are very distinctive in character, and so afford 
ready means of identification. The blunt, curiously shaped jaws (see 
fig. 7) are also characteristic. The hinged body of a click-beetle is 
provided with a tooth which strikes against half of the hinge and 
causes the click that is heard as the beetle springs into the air (see 
PI. II, fig. 4). This tooth when met with in a bird's stomach is often 
:55<>7— No. 15—01 2 
