106 ENTOMOLOGY 
Frequently the wing-covers bulge out to form a resonant cham- 
ber that reinforces the sound. 
The naturalist can recognize many a species of grasshopper 
by its song; Scudder has expressed some of these songs in 
musical notation. The usual song of the common meadow- 
grasshopper, Orchelimum vulgare, may be represented by a 
prolonged zr... sound, followed by a staccato sip-jip-jip- 
i ae 
In Orthoptera, the frequency of stridulation increases with 
the temperature; and the correlation between the two is so 
close that it is easy to compute the temperature from the num- 
ber of calls per minute, by means of formule. The formula 
for a common cricket [probably a species of Gryllus], as given 
by Professor Dolbear, is 
NV — 40 
a 
Here 7 stands for temperature and N, the rate per minute. 
A similar formula for the katydid (Cyrtophyllus perspicil- 
latus), based upon observations made by R. Hayward, would 
be 
1 5 Ob 
pn cote ee 
3 
Here, in computing N, either the “ katy-did” or the “ she- 
did” is taken as a single call. 
Hearing.—There is no doubt that insects can hear. The 
presence of sound-making organs is strong presumptive evi- 
dence that the sense of hearing is present. Female grass- 
hoppers and beetles make locomotor and other responses to 
the sounds of the males, and male grasshoppers will answer 
the counterfeit chirping made with a quill and a file. 
Auditory organs are not restricted to any one region of an 
insect, but occur, according to the species, on antennze, abdo- 
men, legs or elsewhere. 
The antennze of some insects are evidently stimulated by 
certain notes, particularly those made by their own kind. 
Thus the antennz of the male mosquito are auditory, as 
