1926 ] 
Methods of Orientation in Dragon-fly Larvce 
125 
straight course, once turned to the left, again move din a straight 
course once, turned twice to the right, to the left once, moved 
straight ahead once, turned to the right once, and resume 1 the 
straight course five times. An insect with the right eye covered 
entered the light at right angles and at the left of its source. 
This larva turned to the right twice, took one irregular path, 
turned to the right once, to the left twice, to the right once, and 
to the left twenty-one times. When facing away from the source 
of light, it first followed a straight course, and then turned to the 
left twenty times. Facing the light, it turned always to the left. 
Observations based on a study of these larvae in their natural 
habitat or in aquaria gives some clue to the above irregularities. 
The insects are strongly thigmatropic. When a number of them 
are put into a vessel containing nothing but water, they will 
cling to one another until a great mass of intertwined insects is 
formed. This mass is not easily broken by the addition of chem- 
icals, but very warm water will scatter the larvae. Normal- 
ly, these larvae will seek out small sticks or the stems of plants 
and cling to such objects. Usually the entire ventral surface of 
the insect is in contact with this substratum, and the legs sur- 
round it in a close embrace. This brings the long axis of the 
insect’s body parallel to the object upon which it rests. 
The revolving disc that Dolley (1916) used so successfully 
in his experiments on Vanessa antiopa had no influence on the 
young dragon-flies, either in or out of the water. The nature and 
direction of light was a little more effective. Among aquatic 
insects the tactile sense seems to be only a shade less important 
than vision, and in may cases even more important. Anax and 
Aeschna larvae orient primarily through contact stimuli. The 
influence of vision in orientation is secondary. 
Literature. 
Dolley, W. L. 
1916. Reactions to light in the mourning-cloak butterfly, 
Vanessa antiopa. Jour. Exper. Zool. XX, p. 357. 
