SPIDERS AND INSECTS OTHER THAN ANTS 395 



by a sense of direction ; but can hardly be said to have estab- 

 lished this last point experimentally. 



SOUND-PRODUCING ACTIVITIES. 



During the year, Allard (3-7) has produced several papers on 

 the stiidulations of the Orthoptera. In one (4) he gives a gen- 

 eral discussion of the subject and describes methods of study- 

 ing this form of behavior; in the other papers (3, 5, 6, 7) he dis- 

 cusses in detail the sounds produced by a large number of spe- 

 cies. The statements in the remainder of this paragraph are 

 condensed from the paper (4) containing the general discussion. 

 Stridulating powers are highly developed in the Acridiidae, 

 Locustidae and Gryllidae; the last mentioned being the most 

 musical and the first the least. Strident sounds of insects are 

 always of an instrumental and never of a vocal sort. Usually 

 musical sounds are entirely absent ; when present they are 

 usually of a continuous monotonous tone. Except some Acri- 

 diidae, which stridulate by movements of the hind legs against 

 the tegmina, the stridulations of the Orthoptera are produced 

 by definitely controlled movements of the tegmina, which have 

 been modified for that purpose. Among the Acridiidae that 

 stridulate during flight the inner wings are brought against the 

 tegmina at will. Among the more highly specialized Locus- 

 tidae a portion of the base of the tegmina has been modified 

 for sound production. The wings of the Gryllidae show the 

 most complete modification. Entomologists have neglected to 

 study the musical habits of the Orthoptera, hence the stridula- 

 tions of only the common forms are known. Attempts to reduce 

 the sounds to music have not been wholly successful, because 

 the sounds are usually unmusical. All of the Gryllidae, how- 

 ever, have true musical tones. Slight changes in the light, 

 temperature, and moisture have peculiar, but specific, influences 

 upon the character of the stridulation. Forms that in summer 

 stridulate only during the night, in the cool fall often stridulate 

 only during the day. In the summer time, the atmospheric 

 condition preceding a thunder storm at night causes many 

 Orthoptera to be musical until the storm has passed. Marked 

 differences in stridulation may characterize certain species in 

 different parts of their range ; this is especially true of Gryllus 

 pennsylv aniens . 



