CHAPTER VII. 



ANALYSIS OF HETEROGENEITY IN SOME SIMPLEST 

 CHARACTERS. 



ANALYSIS OF HETEROGENEITY IN SOME SIMPLEST COLOR-CHARACTERS. 



It is known beyond doubt that color characters are as fully " law-conforming " 

 in their origin, development, and behavior as structural or physiological 

 features. 



In Leptinotarsa the color-patterns in the species utilized consist of two super- 

 imposed sets of pigments, one in the outer layer of the cuticula, the cuticula 

 pigments, and the other in the tissues of the hypodermis or immediately below it, 

 the hypodermal colors. The relations of these I have described in previous 

 papers. In the formation of color-patterns these two sources of color behave 

 quite independently of each other, the lipoid or hypodermal colors forming the 

 usual color-ground while the cuticular pigments may be either of general distri- 

 bution over the surface, in which case it may hide completely the lipoid color, 

 or in areas arranged in a precise pattern. The latter colors are always dark 

 browns or blacks, rarely light browns or dark yellow, and may belong, though 

 it is by no means certain, to the melanin series of pigments (Gortner), and 

 arise as the result of the action of an enzyme upon the soft primary cuticula, pro- 

 ducing the pigment and the hard outer surface of the integument. The color 

 areas are always developed in precise positions or centers of expression, which, 

 as I have shown, are as fixed in the constitution of the organism as are the rela- 

 tions and positions of nerves or muscles. Many of these areas are simplest 

 characters in that they are indivisible, are present or absent in toto, and invari- 

 able in position. 



I have endeavored to discover what these characters can reveal in the way 

 of concrete information concerning the following problems : 



In simplest characters are the differences : 



(1) Quantitative or qualitative in character? 



(3) Continuous or discontinuous, or both, and what is the relation of the 

 two? 



( 3 ) Delimited or undelimited ? 



(4) Determinate or indeterminate ? In restricted localities and groups ? 



In groups and species of wider range? 



a, in the adult. — The members of the lineata group, save one, all have a spotted 

 pronotum in which the colored areas are developed around a series of centers 

 shown in figure 13. I have elsewhere shown that these centers are invariable in 

 position, but that two or more of them often unite to form a larger color area. 

 Three spots, c, b, d, meet all the requirements of simplest characters in that each 

 is always present or absent in its entirety ; they are never known to break up into 



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