14 Psyche [February 



After they had been in the light a few minutes, I noticed that each 

 and every caterpillar was moving its head up and down with a sort 

 of a twitching motion, in perfect synchronism. These movements 

 occurred at intervals of about two seconds and continued for about 

 five minutes after they were first noted; I cannot say that I saw 

 the beginning of this performance, but all the caterpillars in both 

 cages were moving their heads vigorously when first noted, and at 

 the end the movements stopped gradually until all were at rest. 

 The following night I prepared to resume my observations, this 

 time placing the cages about ten feet apart, but on this occasion 

 during an hour's vigil no movement took place and the second day 

 afterward pupation began. 



Professor Edward S. Morse of Salem and others have observed 

 and recorded the synchronous flashing of thousands of fireflies^ 

 which would not seem to be simply accidental considering the large 

 numbers involved. In conversation with Mr. A. P. Morse of 

 Wellesley, he said that if his recollection was correct, he had seen 

 when a boy synchronous movements in a colonial black and yellow 

 larva on oak, probably a species of Anisota; also in Datana (prob- 

 ably ministra) on black walnut; and in a green and black sawfly 

 larva on gray birch. 



In my observations on the Vanessa antiopa larvae the movements 

 doubtless signified alarm and were possibly protective, but why 

 the alarm shown but once after several weeks of the same routine 

 and then the perfect synchronism in both cages? By a process of 

 elimination in regard to the known sensory equipment of insects, 

 I get no satisfactory results; a floor of wood and tin precludes the 

 use of sight organs, not the least sound could be detected and the 

 slender legs of the upper cage were the only material path excepting 

 the air through which vibrations could be transmitted. 



The theory of vibratory communication would seem the most 

 probable, and if it were known that insects could transmit as well 

 as receive vibratory impressions, it would explain many things. 

 Folsom says of insects: 



"They have many curious integumentary organs which from 

 their structure and nerve connections are probably sensory end 

 organs, though their functions are either doubtful or unknown. 

 Such an organ is the sensillum placodeum — ^function doubtful; 



i Science, July 26, 1918, pp. 92-93. 



