154 COLORATION IN LEPTINOTARSA. 



tinguishable three anterior and three posterior centers, corresponding to the 

 inner, middle, and outer pairs of tergal centers found in the larvae. The inner 

 and outer pairs of centers develop before the middle pair; and lateralward 

 fusions form anterior and posterior bands such as are found in the larvae 

 and in the ontogeny of mclanothorax. These fusions are of exactly the same 

 type as those shown in the abdominal segments of larvae of signaticollis. 



Suggestive also along this same line are stages in the ontogeny of species 

 like violesccus and dilecta, which have a unicolorous pronotum. Stages in the 

 color ontogeny of violesccus are represented on plate 18, figs. 27 to 32, and 

 of dilecta in figs. 33 to 38. Figs. 27 to 29 show features of color levelopment 

 in violesccus comparable with stages found in mclanothorax and to be inter- 

 preted in the same manner. 



Those species of Leptinotarsa which have unicolorous epicrania and pro- 

 nota and some development of chemico-physical colors also present interest- 

 ing stages of growth. Illustrations of the development of the color pattern ot 

 two such species, dilecta and violescens, have already been given and the 

 earlier stages have been discussed. In the later stage the relation of the cutic- 

 ula color to the appearance of the metallic luster of the adult is seen. In the 

 stages shown on plate 18 it is evident that the cuticula color must precede 

 the physical portion of the chemico-physical coloration and must reach a con- 

 siderable degree of intensity before the latter can become visible ; for as the 

 cuticula color gains in intensity and absorptive power the chemico-physical 

 color becomes more and more apparent. 



The Ontogeny of Color on the Wings, 

 on the elytra. 



In Leptinotarsa no color develops on the elytra until after the animal has 

 left the pupal stage and the elytra are fully expanded and possess a relatively 

 firm texture. After their emergence from the pupa and the development of 

 their adult form, these beetles, like most of the Coleoptera, spend many hours 

 and often several days in the absolutely dark pupal cell ; and it is in this period 

 of adolescence that the wing colors are developed. 



The ontogeny of coloration in the elytra of L. undecimlineata is shown on 

 plate 19, figs. 1 to 6. In fig. 1 the elytron is represented as it appears several 

 hours after emergence, when it is of a uniform pale yellow-white with delicate 

 traces of dark color, and when the trachea are well filled with air and stand 

 out conspicuously against the darker opaque body-color beneath. The first 

 well-developed traces of markings are shown in fig. 2, where faint yellow- 

 brown areas of color appear anteriorly in the costal and subcostal spaces and 

 extend distalwards over perhaps one-third the length of the elytron. This 

 color extends posteriorly, deepens rapidly, and also appears in the other inter- 

 spaces of the wing (fig. 2) ; and this process is continued until each of the 



