LIGHT REACTIONS — METABOLISM — MAY-FLY NYMPHS 437 



Some idea of the nature of experimentation together with its 

 effect on the nymphs may be gained from table 4. This table is 

 a slightly expanded copy of a portion of the laboratory record for 

 the day. It shows that during almost four hours of observation, 

 in which time three biometer tests were made, the nymphs 

 maintained their original light reaction and that each test showed 

 the positive nymph had the higher rate of carbon dioxide 

 production. 



Whatever the faults of the method used, it at least has the merit 

 of being always comparative. As was to be expected, large 

 nymphs gave off carbon dioxide more rapidly than small ones and 

 active nymphs more rapidly than inactive ones. These nymphs 

 are strongly thigmotactic, and this usually caused them to remain 

 quietly in their container. Occasionally one would move. Such 

 determinations were of course thrown out. 



PHOTOTAXIS AND CARBON DIOXIDE PRODUCTION IN UNTREATED 



NYMPHS 



These njonphs, like Leptophlebia, are usually negative to light. 

 This normal reaction to light is graphically shown in chart 1 

 together with the preliminary and control records shown in charts 

 2, 3 and 4. 



About 20 per cent of the untreated nymphs were positive to 

 light. When these were tested they were found to have a higher 

 rate of carbon dioxide production than the negative nymphs. 



P 

 Their -j^ ratio, based on 332 non-selected control readings was 5.5 



This is indicated by the graphs in columns 1 and 2 of chart 1 and 

 the details are given in table 5. 



Exposure to light for considerable time sometimes caused 

 negative nymphs to reverse their light reaction and become 

 positive. Such animals were found to be more stimulated, as 

 determined by the rate of carbon dioxide production, than simi- 

 lar nymphs that had not been exposed to light (table 6) . This is 

 just the opposite to the result obtained by MacCurdy with nega- 

 tive starfish which he found gave off less carbon dioxide when 

 exposed to strong light. 



