92 ANIMAL AGGREGATIONS 



tree. From this group, then, the synchronism extends over the entire 

 tree in an irregular wave until all of the insects are flashing in 

 unison. 



"Synchronism usually begins shortly after darkness has set in, the 

 fireflies emerging from the nearby thickets and flying in an indirect 

 course to the Sonneratia trees. During this flight to the trees there 

 is no sign of a concerted flashing, the actions of the insects being 

 similar to those found in our local forms during flight." 



It seems probable that with these fireflies we are dealing with a 

 phenomenon of two distinct aspects (Blair, 19 15). One is a recovery 

 response similar to recovery from fatigue. Such flashing would rarely 

 be synchronous or near-synchronous. On the other hand, there ap- 

 pears to be a releasing stimulus which, in the cases observed by Hess, 

 might come either from the pace-setting flash of a firefly or of an 

 electric torch. This brings up the problem of the leader in group inte- 

 gration, for which we have not space here. It is discussed at some 

 length by Child (1924). 



INTEGRATION BY SOUNDS 



Among many animals group organizations occur as the result of 

 sound production. To be sure of this, one must have evidence that 

 behavior is altered as a result of sounds. The fact that collections 

 of animals, such as frogs or insects, are producing sounds which are 

 loud to the human ear is not good evidence that they have group 

 significance (Lutz, 1924). There is evidence that among some ani- 

 mals sounds may be used in sex recognition. Perhaps they are more 

 often of sexual significance in general sex stimulation which, while of 

 advantage to the group, may yield no advantage to the producer of 

 the sound ; and may even result disastrously in the case of the young 

 deserted by a nesting bird which had been stimulated to renewed 

 sexual activity by an outburst of song. Such cases have been re- 

 ported by creditable ornithologists (Sherman, 1924). 



Ohaus (1899-1900) and Wheeler (1923) report that the Passalus 

 beetles, which have the habit of boring in logs, are kept together by 

 auditory signals; and Professor Wheeler has more than once spoken 

 of his observations, indicating that aerial sounds may play a part in 



