STRUCTURE OF PIGMENTED AREAS. 



That the attachments of the muscles have an influence on the color- 

 pattern of the head and pronotum is probable. I have not felt it neces- 

 sary to go into the matter of structure of these parts in detail, however, 

 because the great range of variation in the color-pattern within a genus, 

 or even within a species, where the structure cowld not differ in any but 

 a slight degree, is such that the influence of structure can be only along 

 narrow lines. 



In the elytra the influence of structure is more evident, but less than 

 might be expected. The sutural margin is thickened and paralleled by a 

 slight groove. As will be seen later, this margin is especially subject to pig- 

 mentation, and this in fact distinguishes several species and varieties. 

 Spots are confluent with it in a few species and may become so by modifi- 

 cation by cold in Hippodamia cowwrfieus. Yet, in general, when spots 

 near the suture enlarge, their margins, which if they remained circular 

 would become tangent to the suture, flatten and become parallel to the 

 suture without touching it. 



Fie. 1. Position of linea interim, liix-a nif<li;t, :md liuea cxtcrna, of: a, d, Adniia: 

 />, f'nci'iiiellit: c, ffiiipotlainia: il, Anulix; e, h'/ii/ac/inn. 



The lateral and basal margin is much modified structurally in variations 

 of germinal origin. It is one of the parts least subject to pigmentation. 

 In modification by cold, however, pigment readily extends along it from 

 neighboring spots. 



In Adah' a three veins are visible, named by Schroeder (1901) linea 

 interna, linea media, and linea externa (fig. 1). The linea externa is 

 quite close to the reflexed margin. It departs farthest at the humeral 

 angle, where it can be most clearly seen. Any other veins that exist 

 must be in the modified and thickened sutural or marginal parts of the 

 elytra. The influence of these lines on the color-pattern of Adalia is 

 considerable, as shown by Schroeder (1901). 



But in Coccinella the linea externa can not be seen in the hardened ely- 

 tron; yet its path can be traced in the basal half of the elytra by the 

 extension of pigment along its course in C. iwvemnotata from the spots 1 

 and 2 along the linea externa. This is farther from the margin than in 

 Adalia. It is probable that there is a vein in the soft elytron, visible evi- 

 dence of which (to the hand-lens) does not persist in the mature wing. 



In Hippodamia also the linea externa is not visible. Its course is out T 

 lined by pigment in cases of modification by cold and in the two wild 



