1950] Edwards and Nutting — Thermobia and Grylloblatta 35 
the heart visible through the mesothorax and first abdominal seg- 
ment. 
The tube containing the insect was placed on a plasticine plat- 
form in a porcelain crucible which could be closed with a loose- 
fitting, transparent cover. The temperature of the air in the chamber 
was taken from a thermometer piercing the cover, (with the bulb 
close to the specimen). Lower temperatures were obtained by sup- 
porting the chamber in a salt and ice water bath. High temperatures 
were furnished by fitting the chamber into the top of a paraffin oven. 
For many of the heart rate counts laboratory light was sufficient; for 
others, a diffuse, water-filtered beam from a microscope lamp was 
directed into the chamber. 
Except at the damaging extremes, Grylloblatta was exposed for 
an average of 17 minutes to each temperature level. Thermobia was 
exposed for an average of one hour and ten minutes at each level. At 
least two readings were made for each temperature, but three or 
many more were made in most cases. No specimens were used for 
further recordings, afer being exposed to temperatures that might 
be considered damaging. In all cases the rates for previously known 
temperature preferenda were obtained before subjecting a few in- 
dividuals to lethal limits. During each run it was frequently noticed 
that struggles or movements of the alimentary tract produced marked 
irregularities or even brief cessations of heart activity. 
Results 
A. Oxygen consumption: 
Grylloblatta. — The oxygen consumption of Grylloblatta at 
various temperature levels throughout the range —2.5° to 20.5°C 
is given in Figure 1. The animals remained active for a number of 
hours at — 5.0°C though the oxygen consumption at that temperature 
was not measurable by the techniques available. The metabolism- 
temperature curve for Grylloblatta is a straight line (Fig. 1), with 
an average Qio of 2.7. With increase in temperature there was a 
regular increase in oxygen consumption up to 20.5 °C. At that tem- 
perature the animals became paralyzed quickly so that a full hour 
exposure was not realized. Subjection of the data to an Arrhenius 
plot gives a temperature characteristic of 14,600 calories over the 
range -2.5° to 20.5°C (Fig. 3). 
At — 5.0°C the animals were active but movement was noticeably 
