GENERAL DISCUSSION. 87 



By the first criterion the Pacific States would be the center of origin of 

 Coccinella trifasciata, but this seems to me the least probable center of 

 origin. In all other localities this wide-ranging beetle is constant to a pat- 

 tern which is present in other species. In the Pacific region it yields to the 

 general tendency there and gives a series of variations towards reduction. 

 The conditions of the criterion are thus fulfilled, but the conclusion does 

 not follow. The position of greatest differentiation is not only a result of 

 time, but also of the diversity and efficiency of the environmental influence. 



The fourth criterion of great abundance is so obviously in the control of 

 the environment and subject to such rapid changes that it is not of aid 

 here. 



Multiple origins must be reckoned with. When the environment is 

 capable of producing changes of the germ-plasm, we may expect similar 

 changes to take place independently throughout the one unit of environ- 

 ment and in other disconnected but similar environment units. Hippoda- 

 mia convergens would probably give rise to var. quinquesignata wherever 

 it encountered mountains in the same general region. 



There is a great wealth of varieties of Hippodamia convergens in the 

 Western States in contrast to a uniform monotony in the Eastern States. 

 The criteria of dispersal would lead us to conclude that the Western States 

 were the center of dispersal, but I think this is not justified. H. conver- 

 gens "flies to pieces" in that region. It would do so at the time of origin 

 if it arose there or at time of entrance into it, if it arose elsewhere. 



We are, then, reduced to a very cautious use of criterion 3 with slight aid 

 from criterion 2. The results are not sufficient to make it possible to 

 reconstruct the dispersal of any species from those here studied, and only 

 one reasonably safe conclusion appeals to me. 



Coccinella novemnotata var. menetriesa and C. transversoguttata are com- 

 mon to eastern Asia and western America. There is a close relation be- 

 tween Hippodamia amoena of Siberia with Hippodamia apicalis of Western 

 America and between Coccinella mannerheimii and Coccinella tricuspisand 

 between Cocinella interrogans and Cocinella sinuata of Asia and America, 

 respectively. Species common to Europe and North America are found in 

 Siberia as well, with the possible exception of Adalia bipunctata, which 

 Leng suggests was introduced into North America. These considerations 

 would lead us to believe that the latest route of dispersal between the 

 Palearctic and Nearctic realms was by the Aleutian or Behring route. I 

 do not believe that we are justified in concluding at present in which direc- 

 tion the greater amount of dispersal took place. 



One expects the different species in a region to occupy different niches 

 in the environment. This at least is a corollary of the current belief that 

 every species is as common as it can be, its numbers being limited only by 

 its food-supply, a belief which is the result of the strong Malthusian lean- 

 ings of Darwin. The major species of the coccinellids do not seem to be 



