84 EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



definite direction. These extensions in the case of most spots are always 

 true in their aim and meet each other exactly. In others, as m and a in 

 Coccinella, the approach is ragged. In those beetles in which the black 

 spots are all confluent one would expect, if confluence were the mere 

 result of overgrowth of pigmented areas, that the light areas thus inclosed 

 and remaining as clear spaces in their turn would have projecting points 

 and concave sides. Such spaces are not wholly unknown, they are illus- 

 trated in one variety of Neoharmonia notulata. But generally such lacunae 

 are rounded, giving rounded spaces with a black background. There 

 must, therefore, be in this case a confluence by definite mutual extension 

 of the spots. 



These orderly extensions point conclusively to determinate variation. 

 But since there is nothing in the structure of the elytra to explain why a 

 spot should be here or there in the cephalo-caudal direction, it seems prob- 

 able that the nature of the determiner-complex for the elytra must be such 

 as to cause variation in these particular set lines rather than haphazard. 



Asymmetrical specimens are not uncommon in looking over large series 

 and are frequently sufficiently marked as to leave no doubt that they are 

 the result of some inequitable distribution of the determining agent, what- 

 ever it be, in development. 



That there are both fluctuations and mutations present in these beetles 

 is probable. But under the name of fluctuations we group three different 

 things. First, there are the modificational differences. Second, varia- 

 tions arise in spite of similar germ-plasm and similar environment, from 

 the difficulty of constructing a soma according to the germinal specifica- 

 tions even with a similar environment. The developmental processes are 

 not adequate to the task of producing exact fac-similes. Third, there are 

 the variations resulting from slight germinal differences. Of these three 

 kinds, only the third is inheritable. All three are to be found in these 

 beetles. Their evolutionary significance is obviously very different. 



MODIFICATION. 



When a full-grown larva of certain species is subjected to certain 

 influences which are maintained through a part of the pupal period, mod- 

 ification of the color-pattern results. But the portion of the color-pattern 

 which responds differs not only with the influence employed, but also with 

 the different species. Thus 40 produces no noticeable effect upon Cycloneda 

 sanguined, Coccinella novemnotata, Megilla maculata, and Hippodamia 

 convergens, nor upon the elytra of Epilachna borealis. But the pronotum 

 of the latter has its pigment very much reduced; in fact, in some speci- 

 mens, to the degree of reduction found in the Texas species Epilachna 

 toweri. Refrigeration does not affect the pigmentation of the elytra, but 

 increases the pigment of the pronotum, though not to a degree comparable 

 to the reduction of pigment by heat. 



