446 WALLACE CRAIG 



Oniy one detailed and exact study of the problem is men- 

 tioned in any of these reports, or is known to the reviewer. It 

 is Shull's* study of the chirping of crickets. Shull timed the 

 chirping accurately in a large number of cases. He verified the 

 law that the rate of chirping increases with the temperature, 

 that at a given temperature nearly all the crickets chirp at 

 almost exactly the same rate, so that there is necessarily a 

 great deal of accidental synchronism. He singled out two 

 individual crickets, to observe whether they really influenced 

 each other and thus produced perfect synchronism, and he gives 

 evidence indicating that this does occur, but the conclusion is 

 stated with some reservation. 



A number of naturalists write of fireflies flashing synchro- 

 nously. But, of the contributors to the present discussion, none 

 had observed this phenomenon more than once; Allard (1), 

 Bumpus (quoted in 7 and in 3), and Morse (6) each had ob- 

 served it once, and not under circumstances favoring critical 

 observation. Blair (2) and McDermott (5) had never seen it 

 themselves. Doctors S. O. Mast, W. M. Wheeler, and F. X. 

 Williams tell me that they have never seen it. Laurent (4) 

 says that many times in his own observations he has proved 

 that what appeared to be synchronous flashing of fireflies was 

 an illusion due to the twitching of his eyelids. And even in 

 the reports that are given, the synchronism is ascribed to a 

 large and indefinite number of fireflies, some reports even state 

 definitely that the synchronism did not include all the indi- 

 viduals; hence none of the observations are known to have 

 been free from the statistical fallacy mentioned above. 



Wheeler (10) believes that a flock of pelicans in flight keep 

 time with each other in their wing beats. In a letter which 

 he kindly wrote to me in answer to inquiry, he says in part: 

 "These birds fly in small flocks of four to eight individuals, if 

 my memory serves me. These flocks are very compact, the 

 birds flying in a single line coincident with the direction of 

 flight, and not oblique as with geese. The beat of the wings 

 was evidently set by the first bird, and sometimes there was an 

 imperfect synchronism until the flock got under way. I am sure 

 that the synchronism was not an illusion. I am also sure that 

 it could not be ascribed to chance." Now, when geese fly in a 



2 Op at. 



