156 JOSEPH HALL BODINE 
An examination of this figure shows several interesting facts, 
the most striking of which is that a difference in rate of OOo 
output is noted between the three species. That such a differ- 
ence is not due to body weight is shown by a comparison of the 
respiratory rates of nymphs of Melanoplus f . rubrum and Dichro- 
morpha viridis, which are of approximately the same weights. 
The most plausible explanation of this fact seems to be that this 
difference corresponds closely with the mode of life of the two 
species, Melanoplus f . rubrum being a very active animal, while 
Dichromorpha viridis is a relatively sluggish one. A point of 
further interest is that the rate of COo output is higher for 
lighter animals and decreases progressively as the animals 
increase in body weight. As it has already been pointed out 
that differences in body weight, especially in nymphs, are closely 
correlated with differences in age, we are led to assume that 
younger individuals have the higher rate of respiratory output. 
Like results are also found for other species. Since differences 
in body weight between males and females exist, the question 
naturally follows as to whether similar differences in the rate 
of COo output are found. Figure 6 shows that males tend to 
have the higher rate. The animals of the two sexes, in this 
case, are of approximately the same age, and differences in weight, 
as shown in a previous section, are due mostly to eggs in the 
female. Whether any fundamental difference in rate of respi- 
ratory exchange exists between the two sexes is somewhat doubt- 
ful, but such differences are reported for other animals, including 
man (Benedict and Emmes, 17). 
b. Rate of output. Much evidence has been accumulated 
concerning higher forms and man to show that smaller individuals 
have a greater respiratory exchange per unit of weight than 
larger ones, and that respiratory exchange is proportional to the 
area of the surface of the body (Rubner, 18). For lower forms 
few such observations exist. Child (19), and Allen (20), for 
example, with Planaria, find that respiratory exchange decreases 
as the size of the worm increases, but give no calculations show- 
ing any possible surface relations. Krogh (21), in summarizing 
work done on lower forms, finds that results are conflicting, and 
