42 
Psyche 
[March 
GROWTH AND DETERMINATE SIZE IN INSECTS 
By Charles T. Brues. 
In common with nearly all metabolic activities, growth is 
essentially a determinate process, and size since it is the 
ultimate result or end product of growth, is inherently 
determinate also. To speak of the determinate size of an 
individual animal is therefore only to restate a self evident 
fact, and he who attempts to expound upon its truth may be 
accused of considerable naivete. During the recent cycle of 
biological investigation much attention has been given to 
the phenomena of growth, especially by physiologists, 
geneticists and statistical biologists. These workers have 
defined in mathematical terms certain of the more evident 
features of growth both in individual organisms and in 
populations, but I believe that it remains for some one more 
deeply interested in another phase of biology, namely tax- 
onomy, to consider size as in a sense a static phenomenon 
in spite of the fact that it is clearly a measure of growth. 
This is particularly appropriate in dealing with insects, 
since in them the growth process is ordinarily very rapid, 
ceasing abruptly and not gradually slowing down. Such 
observations are necessarily less precise than the data just 
mentioned, but they serve to demonstrate the existence of 
a deep-seated and stable genetic constitution which deter- 
mines size and the growth process by which it is attained 
in individual animals. Size as we shall consider it, results 
from the interaction of a series of excitatory and inhibitory 
stimuli during the development of an individual whereby 
its growth follows quite closely a definite and predictable 
course, terminating when adult size is attained. Such 
termination is particularly definite in the case of insects 
where almost without exception the imaginal or reproduc- 
tive stage marks sharply the attainment of final size and 
form. 
