I32 COLORATION IN LEPTINOTARSA. 



THE DEVELOPMENT OF COLORS IN LEPTINOTAESA. 



CHEMICAL OR PIGMENTAL COLORS. 



The most important of the chemical colors are those located in the cuticula 

 and in the hypodermis. In the ontogeny of the animal, however, the cuticula 

 colors are lost at each ecdysis, and are replaced by new developments thereof, 

 whereas the hypodermal colors persist from larva to adult. In this account 

 we shall first consider the development of the cuticula colors and the struc- 

 tures that carry them. 



CUTICULA COLORS. 



A section through the body wall of these beetles in any stage shows the 

 following structures : On the outside is the primary cuticula, a layer of hard, 

 homogeneous, unstratified material, everywhere of uniform thickness, not 

 penetrated by pore canals, and carrying deep brown or yellowish diffuse cuti- 

 cula pigments. Beneath this is a layer of varying thickness, composed of 

 alternating layers of material having different refractive indices, and pene- 

 trated everywhere by minute pore canals, which reach outward to the edge of 

 the primary cuticula. This layer is devoid of pigment, except in rare cases, 

 and is always unpigmented in Leptinotarsa. The inner surface of this cuti- 

 cula, the secondary cuticula, is uneven. Into the uneven places the hypoder- 

 mal cells fit exactly, and from them send out long, delicate, protoplasmic pro- 

 cesses, which fill the pore canals in life. The cells of the hypodermis vary in 

 size and shape according to their position in the body and the ontogenetic 

 stage of development in the individual. They are, however, always columnar, 

 and are backed up on the inner surface by a delicate layer of mesodermal 

 cells, endothelium, which lines the body cavity. In these hypodermal cells 

 are found the granules of the hypodermal pigment and beneath them the dif- 

 fuse subhypodermal color. 



During the ontogeny of these beetles the integument undergoes a series of 

 cycles of development whereby the cuticula colors are lost and redeveloped 

 several times. These cycles of development are associated with ecdysis, and 

 are important for the understanding of color ontogeny, especially that in the 



larvae. 



In the embryo, at about the end of the embryonic period, the cells of the 

 hypodermis (ectodermal cells) secrete rapidly an even, homogeneous layer of 

 cuticula over the entire surface. This layer is without visible structure, 

 stains intensely in many stains, and is soft and pliable. No colors are seen at 

 first ; but in the few hours immediately preceding hatching color develops, at 

 first as faint yellowish or opaque areas. These later change to a light yellow- 

 brown, and remain so until after hatching, when they rapidly become darker, 

 and finally black. These darker areas constitute the colors "proper to the 



