STUDIES OF VARIATION IN INSECTS 325 



variation can be attained by controlling the environment (kind 

 and quantity of food, degree of temperature, humidity, light, 

 etc.), but if such variations (modifications) acquired during 

 development are not inherited, there will be no advance gener- 

 ation after generation along any certain line. There will be no 

 cumulative effect of such determinate variation. The constant 

 repetition of a certain environment on generation after genera- 

 tion of a certain species would of course produce a constant 

 repetition of certain individual modifications (orthoplacy), but 

 we do not know as yet of any actual effect on the species of 

 such persistent ontogenic variations. 



The need, however, for some such factor in species-forming 

 as determinate variation is obvious and strongly felt. There 

 are certainly few selectionists left who honestly believe that the 

 minute fluctuating variations in pattern, in size, in curve of a 

 vein, in length of a hair, etc., have that life and death value 

 which is the sole sort of value that an " advantageous varia- 

 tion " must have to be a serviceable handle for the action of 

 natural selection. As a matter of fact, no systematist will have 

 escaped having had it distinctly impressed on him that he rec- 

 ognizes differences in the pattern of lady-bird beetles, in the 

 number of fin rays in fishes, in the branching of a vein in flies' 

 wings, that no enemy, no agent of natural selection, can recog- 

 nize, at least to the extent of pronouncing sentence of death (or 

 not pronouncing it) on its basis. And further, no biologist 

 really satisfies himself with the worn statement, " We must not 

 presume to judge the value of these trivial, these microscopic 

 differences, for we do not know all the complex interrelation 

 and interaction of the organism and its environment." We 

 do not, but we do know for many cases that such differences 

 are actually not of life and death selective value, and reason- 

 ing compels us to believe to a moral certainty that in other 

 cases these fortuitous trivialities have similar lack of life and 

 death importance. The case of the variation of the convergent 

 lady-bird beetle, Hifpodmmia convergens (p. 257 et seq.) is 

 distinctly in point. In our account of this variation we have 

 called attention to the suggestiveness, in its light on the rigor of 

 the " struggle for existence" among individuals, of the fact that 



