GENERAL DISCUSSION. 97 



affected. No reaction may result, comparable ones may result, or wholly 

 different ones may result, and besides, different degrees of the heat may 

 be necessary to give any of these results. 



AdaUa bipunotata in Europe has many varieties, modified in the direction 

 of greater pigment, and many of them are found in any one locality ( Weis- 

 ner, 1907) , yet in America this species is relatively constant. Coccinella 

 perptexa and its very close European ally, C. trifasciata, with an elytral 

 pattern practically identical, are quite constant, except in the Pacific 

 States, where there are many varieties of reduction. Hippodamia par- 

 enthesis maintains a greater constancy in the Western States, where so 

 many species become especially prolific in varieties than it does in the 

 Eastern States. 



In the Eastern States most of the species do not find the conditions 

 such as to set up new variation lines. Yet Coccinella novemnotata gives 

 us its varieties of vittation in the East, and throughout the Plateau and 

 Pacific States it offers no varieties but those of reduction. Megilla macu- 

 lata and Xacmia seriata suffer reduction of spots in the Southwestern 

 States, where the other species are also thus affected. Hippodamia api- 

 calis suffers a greater reduction in Eastern Colorado than in the Pacific 

 region. 



Determinate variation governs the birth of a variety, but its later 

 career is governed largely by its method of inheritance and by natural 

 selection. If the variety is subponderant, it will probably take the status 

 of a rarity, arising again and again by the determinate variation but 

 never winning an important place. It is possible that subponderance in 

 some characters is capable of being converted into preponderance by selec- 

 tion or by the action of environment on the germ-plasm and a place thus 

 acquired by it. In others their subponderance may be expected to be fun- 

 damental and unalterable. If the characteristic be preponderant, its way 

 is made smoother, and if determinate variation cooperates by frequently 

 offering the variation, the characteristic is sure to make its way unless 

 opposed strongly by natural selection. If it arises very rarely, its fate is 

 in jeopardy. A mutation which arises only once has a very small chance 

 of success. The frequency with which it arises is an important element 

 in its fate. 



This analysis is carried further in table 21. We see, in examining this 

 table, why a variety aided by determinate variation does not always sup- 

 plant the species, but often reaches a status of a certain degree of relative 

 abundance which it may retain for a long time. Thus in Oregon the vari- 

 ety of Hippodamia convergem with open pronotum continues to exist as a 

 rarity, avoiding extermination on the one hand and increase on the other, 

 because it is kept in existence by determinate variation, and, as I believe, 

 is kept repressed by its subponderance. Since the activity of natural 

 selection, determinate variation, and preponderance are each found in 



