14 THE RELATION OF SPARROWS TO AGRICULTURE. 
broken <>IT from the body, and is sometimes all that is lefl to show 
that a click-beetle lias been eaten. The pitted, earthenware-like wing- 
covers Of weevils (see IM. II, fig. 7) and the curved, sharp jaws of 
ground-beetle Larvae are easily recognizable (see Pi. II, n«r. 7). The 
identification of Bymenoptera is much more difficult, as the distin- 
guishing features are found mostly in the veining of the delicate 
wrings, which are exceedingly perishable. Ants, however, can always 
be recognized by the very hard jaws even when the action of the 
stomach has practically reduced the insect to dust (see PL II, fig. !)). 
Certain black wasps (Tiphia inornata) often eaten by birds may 
be recognized in the stomach by the presence of a 
tiny piece of the crust of the insect's back (ineso- 
thorax), which is sculptured by three parallel raised 
ridges (see PI. II, ii<r. lO). Th(» presence of female 
May-flies can usually be detected by means of the 
prettily reticulated eggs from within the insect's body 
Fl<i 'sU'.r S '' and fche & olden glODUleof oil each contains (see PI. II, 
fig. 11). Bugs (Heteroptera) may be determined by 
their back shields (scutella), which are marked with dark dots and in 
shape closely resemble equilateral triangles (see PI. II, fig. 12); spi- 
ders by their jaws, which look like miniature cow horns, and their 
minute eyes, which resemble clusters of gleaining <jvms (see fig. 8). 
The remains of earthworms are identified with the compound micro- 
scope, the high-power lenses of which reveal the characteristic 
amber-colored S-shaped spicules (see fig. 9) with which the bodies 
of the worms are beset. These lenses are also employed in identify- 
ing bits of the skin of limits and pasty masses of the endosperm, 
or meaty part, of seeds. Differences can thus be perceived in the 
st met ure of the epidermis of many fruits (see PI. Ill, figs. 1 and 5 ) and 
the starch grains of common cereals (see PI. Ill, figs. 1, 
2, and .'}). When a bird has eaten poison ivy there often ^\ 
remains nothing of the fruit except certain black, club- 
shaped bodies (see PI. Ill, fi J_r. 6) which coat the stone 
below the white skin of the fruit. The stones of bay- 
berries are similarly covered with small granules (see ^ 
PI. Ill, figs. 7 and 8), which furnish the clew in each Fia. 8 spicule 
ht , , of earthworm. 
en the stones are absent. 
Alter each element in a bird's stomach has been identified and 
placed in a separate pile, the percentages of the different elements 
are estimated by volume. 1 In recording the results of examinations 
a separate record is made for each species and for each month. 
Monthly averages are based on the Dumber of stomachs collected in 
1 Of course it must be understood that mathematical exactness is not attainable 
in these examinations; but every possible means is taken to reduce the error to a 
minimum, and with a sufficient nnmberof stomachs a very correct idea ma) be 
obtained of the proportions of the different elements of the food. 
