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



doubtful. It is clearly inadequate to produce characters like the extensa 

 mark or the spot q, which environment could not produce acting upon the 

 soma alone. Further, many of the somatogenic characters do not become 

 germinal, as the dark linea externa in Hippodamia convergens. On the 

 other hand, we have seen, in studying the variation and heredity of the 

 markings, evidence of determinate variation and of preponderance. It is 

 to this first factor, aided, I believe, by the second, that this evolution is to 

 be attributed. Since their action is analogous, I have grouped them under 

 the name of determinate evolution in the title of this paper. 



Determinate variation is a dual process, for although the environment 

 frequently causes certain variations, as will be shown later, the nature of 

 the germ-plasm is a more important element in determining whether there 

 shall be any variation formed and what it shall be. In other cases the 

 environmental control of the germinal change is so minor a feature that it 

 is negligible and the cause may be said to lie in the nature of the germ- 

 plasm. The relative roles of environment and the constitution of the 

 germ-plasm are interesting in the case of disappearance of spots, where 

 we found in one environment one spot especially disposed to disappear- 

 ance, whereas in another environment it is another spot (fig. 17). The 

 role of the environment is shown in the following cases: On the Pacific 

 coast, outside of the mountains and the humid coast region, there is a 

 strong tendency to disappearance of spots, five species yielding to this 

 tendency. In the mountains, transverse confluence reigns. In the humid 

 Pacific coast region Hippodamia convergens gives us the very dark variety 

 moesta. It is possible that marshes evoke vittation, for Hippodamia sin- 

 uata (trivittata) is a marsh-dweller, as is Paranaemia vittigera, while 

 Naemia seriata is maritime; but this must be further investigated. Arid 

 regions lead to the reduction of spots, although the greatest proportion of 

 spotless individuals is not found in the region of greatest aridity. 



Where two species are affected by one of these environments, we should 

 get corresponding results. This is realized in the Cascade Mountains, 

 where we have the barred Hippodamia oregonensis, a derivative of H. 

 spuria, and the barred variety quinquesignata from H. convergens. In the 

 Hudson Bay region, with the vittate H. falcigera we get the vittate deriv- 

 ative of H. tredecimpunctataihe Hippodamia americana. 



In the Pacific coast region outside of the mountains and in the humid 

 region, spotlessness is found in Hippodamia convergens obsoleta, H. tre- 

 decimpunctata var. immaculata, Coccinella perplexa var. subversa, Coc- 

 cinella novemnotata var. jranciscana, and Coccinella californica, probably 

 a spotless derivative of Coccinella transversoguttata. Yet it should be 

 mentioned that Hippodamia parenthesis, apicalis, and spuria resist the 

 general trend towards spotlessness. 



The role of the environment must not be overemphasized, for its part 

 may be likened figuratively to the heat that starts a chemical reaction. 

 Where heat is applied, the result differs with the different chemicals 



