go ANIMAL AGGREGATIONS 



frequently tightly clasp any moving object, whether salamander, 

 fish, or other males; and this reaction is based at least in part on 

 sight. Aggregations of young catfishes are primarily integrated by 

 sight and secondarily by water vibrations and chemical-touch sen- 

 sations (Bowen, 1930). 



Other instances might be multiplied; but one spectacular one, that 

 of the synchronous flashing of fireflies, must sufiice. A considerable 

 controversy has been waged over this subject, but the observation 

 experiments of Hess (1920) seem to have established the fact of its 

 occurrence. He found a valley of fireflies flashing in unison, with the 

 flash apparently initiated on a hill at one side, from which it spread 

 almost instantaneously over the valley. The next night in the same 

 place the observer was able to obtain at least partial control of the 

 flash and to alter to some extent the intervals between flashes. With 

 a pocket flashlight he gave the initiating signal just before it would 

 normally have occurred, and the insects followed the artificial lead 

 until the interval was reduced to three-quarters its original duration, 

 and then one-half. At the second trial at one-half the original period 

 fewer insects followed the flashlight, and after that the flashing in 

 unison was broken. 



Such synchronous flashings of fireflies are apparently more com- 

 mon in the orient. Morrison (1929) has published a recent note upon 

 their occurrence in Siam, based upon three years' experience there. 

 His account follows: 



"During the months of July, August, September, and until the 

 heavy rains set in, on any dark night it is possible to see whole 

 stretches of the river or canal banks fit up by the flashing of myriads 

 of insects. These areas of synchronism may extend for several hun- 

 dred yards at a stretch or may be confined to single trees, glowing 

 and being extinguished with surprising regularity. Actual timing of 

 this intermittence showed that luminescence occurs at the rate of 

 approximately 120 times a minute. During the period between the 

 flashes the light of the fireflies reached almost complete extinction, 

 the intensity being so low that at a few feet from a tree of actively 

 luminescing insects it is quite invisible. 



"Perhaps one of the first things which is called to the attention of 



