1 90 ENTOMOLOGY 



positions parallel with the end of the elytron characterize modifications 

 of markings. The response to stimuli (high temperature) is in the 

 same direction. 



Response to other stimuli appears to be in the direction of 

 concentric extension of the markings. 



The color patterns and structure to which they are related constitute 

 a mechanism, the directions of movement of which are limited, i.e., 

 easier in some directions than others; the color pattern plans break 

 when the related structures do; hereditary changes and fluctuations 

 due to stimulation during ontogeny are in the same direction; laws 

 governing the mechanism are the same throughout. 



Variations in general fall into two classes: continuous (individual 

 variations) and discontinuous (mutations) . The former are always pres- 

 ent, are slight in extent and intergrade with one another; they are 

 distributed symmetrically about a mean condition. The latter are 

 occasional, of considerable extent and sharply separated from the 

 normal condition. 



R. H. Johnson published an important statistical study on evo- 

 lution in the color pattern of the lady-beetles. He found both con- 

 tinuous and discontinuous variations present; that the color pattern is 

 capable of modification by the environment; that some modifications 

 are hereditary characters and others not. 



Replacements. Examples of the replacement of one color by 

 another are familiar to all collectors. The red of Vanessa atalanta and 

 Coccinellidae may be replaced by yellow. These two colors in many 

 butterflies and beetles are due to pigments that are closely related to 

 each other chemically. Thus in the chrysomelid Lina lapponica 

 the beetle at emergence is pale but soon becomes yellow with black 

 markings, and after several hours, under the influence of sunlight, the 

 yellow changes to red ; the change may be prevented, however, by keep- 

 ing the beetle in the dark. After death, the red fades back through 

 orange to yellow, especially as the result of exposure to sunlight. 

 Yellow in place of red, then, may be attributed to an arrested develop- 

 ment of pigment in the living insect and to a process of reduction in the 

 dead insect, metabolism having ceased. 



Yellow and green are similarly related. ' The stripes of Poecilocapsus 

 lineatus are yellow before they become green, and after death fade back 

 to yellow. As the green pigment in most, if not all, phytophagous in- 

 sects is chlorophyll, these color changes are probably similar to those 

 that occur in leaves. Leaves grown in darkness are yellow, from the 



