WATER CONTENT AND RATE OF METAB0LIS:M 
155 
higher respiratory rates. It is of importance, however, to 
mention here that most of the work heretofore done on insects 
has been concerned with masses rather than with individuals, 
and that Httle consideration has been given to results obtained 
for different species of the same general group, for different sexes, 
and for animals of different ages. The present discussion deals 
with the carbon-dioxide output of individual animals of different 
Fig. 4 Curves show the rate of COo output per gram per hour for nymphs of 
Melanoplus f. rubrum and Dichromorpha viridis and for adults of Melanoplus 
difTerentialis. Abscissas represent body weights in grams. Ordinates repre- 
sent rates of CO2 output in grams CO2 per gram total body weight per hour, for 
the three species. For further explanation see text. 
species, different ages, and of different sexes, under normal as 
well as experimental conditions. The following species of grass- 
hoppers were studied: nymphs of Melanoplus f. rubrum and 
Dichromorpha viridis and adults of jNIelanoplus differentialis. 
a. Carbon-dioxide output of normal animals. The number of 
individuals studied is, for nymphs of Melanoplus f. rubrum, 350; 
for nymphs of Dichromorpha viridis 300, and for adults of Melano- 
plus differentialis, 85. Figure 4 shows the average rates of 
carbon-dioxide output per gram per hour for these animals. 
