so ILLINOIS BIOLOGICAL MONOGRAPHS (292 



negative response to light. The author knows of no other natural factor 

 calling forth such immediate and pronounced response. These experiments 

 have been performed, therefore, in the following manner: 



An ordinary fifty watt electric light bulb was suspended above the 

 center of a glass-jar three inches in diameter, containing soil, with the 

 lowest point of the bulb six inches above the soil. A thermometer was sus- 

 pended with its bulb touching the soil in the center of the jar. The typical 

 black earth of Illinois was used in a finely pulverized condition and suffi- 

 ciently humid to eliminate dust. It was packed down lightly on top, 

 leaving an even surface. The temperatures ranged from 33.3 to 35.5 

 degrees C. which was much higher than that of the laboratory due to the 

 heat from the light. Except in Experiment 3 all material used was reared 

 outside under approximately natural conditions and well fed. It was not 

 brought into the laboratory until immediately before the experiment was 

 to be started, except in Experiment 3. To avoid interference with one 

 another, not more than five larvae were put together in the same jar. 

 Frequently several instars of the same species were used, allho they always 

 reacted alike, so far as could be observed. Observations were taken every 

 few minutes, account being kept of the time required for the larvae to 

 become visibly stimulated, as well as of the time elapsed before each 

 individual should become buried, wholly or partially. These experiments 

 were performed in April and May, except where otherwise indicated in the 

 tables, consequently the temperatures to which the larvae were subjected 

 during the experiments were unnaturally high, probably adding to the 

 irritation produced by the light. 



It has been shown that stimulation is usually immediate. Well fed 

 larvae, which lie motionless when brought into the laboratory from the 

 outside, generally exhibit pronounced irritation as soon as subjected to the 

 light, running rapidly about the jar. The phrase "time required for sub- 

 mergence" expresses the time from the beginning of activity to the time 

 when the individual is entirely or partially buried. In several instances 

 certain individuals ceased activity as soon as the head and thorax were 

 beneath the surface. This feature seems to be an individual rather than a 

 specific trait. While the larvae of some species commence burrowing within 

 two or three minutes after they become stimulated, entering the soil per- 

 pendicularly and disappearing within a few seconds after they begin to dig, 

 others crawl for half an hour, making an occasional abortive attempt to 

 thrust their heads beneath the earth, finally very gradually burying them- 

 selves by entering the soil at a small angle with the surface. Other species 

 make no attempt to burrow, continuing to crawl actively about for two 

 hours, at the end of which time the experiments were usually ended. We 

 find represented in these species evidently several stages in the development 

 of the subterranean habit, some entering the soil very readily, others with 

 apparent reluctance, and some not at all. 



