144 EVOLUTION AND ANIMAL LIFE 



insects with complete metamorpliosis — and the insects of this category 

 include all the beetles (Coleoptera), two-winged flies (Diptera), moths 

 and butterflies (Lepidoptera), ants, bees, wasps, gall flies and ich- 

 neumons (Hymenoptera), and some other orders — are exposed during 

 their development to just one type of extrinsic influences, namely 

 those of nutrition, temperature, humidity, etc. These influenceG 

 affect the whole body and metaboHsm of the body-developing insect. 

 But they have no direct relation to specific parts. 



"An important special environing condition of life, and one that 

 certainly works direct and obvious influence on the body wall of certain 

 animals, is what may be called the chromatic condition of the environ- 

 ment. Color and pattern adapted to the needs of protection or ag- 

 gression are phenomena familiar throughout the animal series. Most 

 of such color and pattern conditions, catalogued under the head of 

 protective resemblance, mimicry, warning colors, etc., are fixed con- 

 ditions as far as the individual is concerned, presumably brought 

 about by the age-long action of natural selection. 



''Not a few animals display the capabihties of achieving marked 

 adaptive changes, i. e., acciuired variations, during their immature life 

 (postembryonic development). But it is obvious that insects of com- 

 plete metamorphosis, which possess in adult stage a color scheme and 

 pattern wholly different from that of the larva or pupa and one which 

 is not apparent until it appears in fixed definitive condition on the 

 emergence (and drying) of the imago from the pupal cuticle, cannot be 

 conceived to show, in their color pattern, variations due to individual 

 adaptive changes. That is, variations in this color pattern among the 

 individuals of a species are not acquired, but are strictly congenital, 

 except in so far as they are produced by the general influences of 

 nutrition, temperature, etc., working without reference to the external 

 chromatic conditions of the environment. 



''Even such all-pervading influences as nutrition, temperature, 

 humidity, and light maj^ be, and in many cases obviously are, so nearly 

 practically identical for all the members of one brood, or even for all 

 the individuals of the species, that they can have little or no influence 

 in causing variations. For conspicuous example, the case of the honey 

 bee may be noted. Here, all the larvae live side by side under identical 

 conditions (those of the hive) of temperature, humidity, and light, and 

 the distribution of exactly similar food to them in similar quantity is 

 probably as nearly exactly uniform as could be guaranteed under our 

 most careful artificial experimental conditions. The pupae are, more- 

 over, under identical conditions of temperature, moisture, and light, so 



