CHAPTER III. 

 COLORATION IN LEPTINOTARSA. 



In this chapter, which deals with the colors and color patterns in the genus 

 Leptinotarsa, I have attempted to follow the development of the color phe- 

 nomena, both ontogeneticaily and phylogenetically, and to determine the laws 

 by which they are controlled and the environmental factors by which they are 

 modified. 



COLOR PHENOMENA IN INSECTS. 

 COLOR CLASSES. 



The colors of insects are divided into three chief categories, dependent upon 

 the causes by which they are produced. These classes of color we designate 

 as chemical or pigmental, physical or structural, and chemico-physical or 

 combination. 



CHEMICAL OR PIGMENTAL COLORS. 



These colors owe their existence to the presence of a substance of a definite 

 chemical composition, which has the property of absorbing some wave-lengths 

 of light and of reflecting others. These compounds may be the product of 

 the metabolism of the animal, or derived from the food (Poulton, 1893), or 

 they may be accidental inclusions. They may also be colored substances or 

 coloring substances. The colors due to this cause are black, brown, orange, 

 yellow, drab, many reds, rarely blue, green, and white. The pigments which 

 produce them are soluble in various reagents. 



It has been shown that the color-producing substances may be divided into 

 three main classes, which differ in their location in the body and in chemical 

 composition. It was demonstrated by Hagen that these color-producing sub- 

 stances are divisible into two classes, the dermal and the hypodermal, the der- 

 mal being located in the cuticula and the hypodermal in the cells of the hypo- 

 dermis. Poulton and others have shown the existence of color-producing 

 substances in the fat body and haemolymph. These I have called subhypo- 

 dermal colors. The dermal colors and the substances which produce them 

 are located in the outer portion of the cuticula, and are diffuse pigments, and 

 not present in the form of granules, as maintained by Hagen and Enteman. 

 The hypodermal colors have been shown to be usually in the form of granules 

 located in the hypodermal cells, or, more rarely, derived pigments. 



The solubility of these pigments has been studied by Coste, Urech, Mayer, 

 Tower, and Enteman. From these researches it appears that the color- 

 producing compounds are all soluble, but not with the same degree of ease. 



121 



