LIGHT REACTIONS METABOLISM — MAY-FLY NYMPHS 435 



n^'Diph belonging to the Heptageninae. These nymphs are 

 quite common in Pettibone Creek (Shelford, '13, maps) where 

 they are usually found in the stones between riffles. Pettibone 

 Creek is a brook about the same size as the Berkshire streams 

 mentioned in the preceding part, but with much less rapid current. 



The nymphs were kept in the laboratory for long intervals 

 during the winter in well aerated running-water aquaria. Ani- 

 mals to be experimented on were transferred to room-tempera- 

 ture aquaria aerated by means of an air-pressure pump operated 

 by water pressure. 



The experiments were conducted as at Williamstown save that 

 a daylight, concentrated filament, 100-watt Mazda (C2 of the 

 General Electrical Company) was used as a source light. The 

 experimental box was placed in a darkened room so that only 

 light from the source lamp could enter during the experiment. 



In most of this work an assistant plotted the reactions of 

 individual nymphs to light and manipulated their change to 

 experimental solutions. Careful controls were run. When the 

 nymphs were to be changed to a new experimental solution, the 

 controls were changed in the same manner to fresh tap water. 

 The assistant also prepared the pairs of nymphs for their carbon 

 dioxide test in such a way that the experimenter had no idea 

 which was the experimental and which the control nymph. 



The carbon dioxide production w^as determined in Tashiro's 

 biometer (Tashiro, '13, '17) as follows: The assistant placed two 

 nymphs, whose rate of carbon dioxide production was to be com- 

 pared, momentarily on filter paper and then transferred each to 

 "a shallow glass cell. 



The nymphs used were of the same size and were selected so 

 that the experimental factor was the only known cause for varia- 

 tion in their rate of carbon dioxide production. The containers 

 were marked for future identification. These were handed to 

 the experimenter and immediately placed in the apparatus. 

 Within five minutes from their removal from the experimental 

 dishes one could get an indication of their relative rate of carbon 

 dioxide production. Under optimum conditions the entire 

 process of determination could be repeated at the rate of three 

 per hour. This was much in excess of the usual rate. 



