The problem of populations and their fluctuations is of primary importance in ecology. I n order to evaluate the effects of the environment it is necessary to know how much the development of the organism will vary when the environmental conditions are maintained as constant as possible. The senior author has shown (Chapman, '28) that populations of the confused flour beetle, Tribolium confusum Duval, rise to a saturation point and that this point is independent of the size of the environment or the original population. Since then others have used this species for population studies (Gause, '31 ; Volterra, '31 ; Park, '32 ; Stanley, '32 ; Holdaway, '32).
I n order to analyze the effect of an environment on an organism, or to predict the level to which the population of the organism may rise, it is necessary to determine certain biotic constants of the organism (Chapman, '31 ; Stanley, '32) which have to do with the rates of reproduction and development. A 'constant' is usually defined, in the physical sense, as "any property of a subject, numerically determined, which remains always the same under the same conditions." The question before us then is whether or not these biotic characteristics of organisms remain always the same under the same conditions, and whether or not these conditions can be produced and the biotic characteristics measured and Published as paper no. 1213 of the Scieiitific Journal Series of the Minnesota *Doctor Chapman is now dean of the Graduate School of Tropical Agriculture, Agricultural Experiment Station.