PHOTOPERIODIC CONTROL OF DIAPAUSE 603 



(except for Experiment 9 described below). Larvae collected during 

 the nondiapause period were held on a diapause-inducing photoperiod 

 (11 hr) until at least a week after all pupations had stopped, which 

 generally occurred within one month. Larvae collected during the 

 diapause period were available immediately for experimentation. 



Mass cultures were held on an 1 1 -hr photoperiod in loosely covered 

 20-cm finger bowls. Larvae in experiments were cultured in covered 

 stender dishes (6 cm) containing water from pitcher plants 0.5 cm 

 deep; ten larvae were placed in each container, and unless otherwise 

 indicated, twenty larvae constituted an experimental group. Experi- 

 mental larvae were distributed at random to the culture dishes, and 

 dishes were assigned to groups by turning cards. In all experiments 

 a record was made of every pupation and of the day on which it 

 occurred; pupae were removed from the dishes after being counted. 

 Results are given as percent pupation of survivors. A few individuals 

 died in nearly every experiment, but fatalities were apparently at 

 random and usually few in number. Commercially available dried 

 daphnia proved to be satisfactory as food. A thick mixture of ground 

 daphnia was made with pitcher-plant water, and the capacity of one 

 medicine dropper of this mixture was given once a week to each mass 

 culture bowl. One drop of the food mixture was added weekly to each 

 container of experimental larvae (except in Experiment 8 described 

 below). Mass cultures and most experimental groups were maintained 

 in lightproof cabinets located in a controlled temperature room at 

 about 23 °C; when closed, air from the room was circulated through 

 the cabinets by means of a centrifugal fan and a system of lightproof 

 ducts, thus preventing a significant rise in temperature even when 

 lights in the chambers were turned on. Maximum variation between 

 groups was generally within ±:1°C. The results of temperature studies 

 described in this paper make it clear that these small temperature 

 variations were insignificant in accounting for results obtained at 

 different photoperiods. Light intensity at the level of the dishes in the 

 cabinets was 35-45 ft-c. supplied by two 30-watt dayhght fluorescent 

 lamps operated by automatic time switches; ballasts for the lamps 

 were mounted outside the cabinets to minimize heating further. 



Experiments to determine critical photoperiods were conducted in 

 a cabinet containing boxes into each of which a different day length 



