220 THE CANADIAN ENTOMOLOGiST. 



instructive should be Nos. 7 and 8, representing the extremes of wing- 

 length. In neither case is the deviation from the average rate as marked 

 as in some cases where the wing-length is more nearly the average, for 

 example, Nos. 4 and 9. 



c. — Effect of Humidity on Rate. 

 As I was not properly equipped with apparatus, I have no conclusive 

 evidence of the effect of humidity. Eat the results of two sets of observa- 

 tions made on the same evening, under different conditions, point to a 

 probable influence of humidity. The fiVst observations were made under 

 a clear sky, and with no perceptible air currents. Dew was forming near 

 the ground, showing that the vapour was saturated there, while higher up 

 the bushes were dry. The second set of observations was made nearly 

 two hours later, when there were light winds and it was beginning to rain. 

 At this time the vapour must have been saturated at all elevaiions. Hence 

 the humidity had remained constant near the ground, but had risen 

 noticeably at greater elevations. During the two hours the temperature 

 at an elevation of 6 ft. had fallen i°.6. The decrease at 12 ft. was 

 probably about 2°. 2. The crickets observed were in precisely the sanre 

 locations in both sets of observations, and were probably the same crickets. 

 The rate of chirping of those near the ground had decreased 5 or 6 per 

 minute, that at 12 ft. had decreased 20 per minute. Change in tempera- 

 ture alone accounts, according to Dolbear's formula, for a decrease of but 

 9 in rate. It is possible to explain the further decrease at llie higher 

 elevation by supposing that increase of humidity diminishes the rate of 

 stridulation. This supposition will also explain part of the difference in 

 rate noted between crickets at elevations of 2 ft. and 10 ft. on Sept. 7 

 (Table I), since the humidity is greater near the ground. 



d. — Effect of Individuality on Rate. 

 As I did not find external factors to explain satisfactorily all the 

 observed facts, I was led to look for internal factors. Of these internal 

 factors, individuality and physiological state suggested themselves. By 

 individuality is meant that constitutional peculiarity which results in a 

 constant difference between one cricket and its fellows. The constant 

 difference was frequently one of pitch. Certain crickets, while maintaining 

 approximately the same rate, were found to chirp at a constantly lower 

 ])itch than other crickets in similar locations. Again, some crickets 

 possessed a peculiar variety of chirp, one of which is later to be mentioned 

 specifically, and this peculiarity was present in every chirp. If it should 

 be found that each individual, wliile varying its rate with the temperature 



