GENERAL DISCUSSION. 85 



In the Hippodamia convergens, on the other hand, both pronotum and 

 elytra have the pigment increased by the same degree of cold and unin- 

 fluenced by the same degree of heat. The use of various other influences 

 on these and other species produces no effect. Modifiability of this or 

 that feature is then itself a characteristic. It is a characteristic some- 

 times gained and sometimes lost, sometimes always firmly coupled with 

 the feature in question, and sometimes never possessed by it. 



The result has been spoken of as increase and decrease of pigment. We 

 have seen that this may not apply at the same time to both pronotum and 

 elytra. Even in one organ, while modification manifests slight influences 

 merely in the diameter of the several spots or marks, with a stronger 

 influence the additional pigment is laid down in certain directions rather 

 than in others. The result is that the pattern is not merely darkened: it 

 is changed. 



The interesting question arises, Are these changes identical with hered- 

 itary changes in phytogeny or something quite different? Some are clearly 

 identical, such as the lateral process of the pronotum of Hippodamia con- 

 icns, and some are clearly different from any hereditary condition 

 known, as shown in fig. 26. 



If we examine these two categories carefully, a generalization is possi- 

 ble. The influence of structure is frequently obvious in characteristics 

 which are the result of modification, much less frequently so in hereditary 

 conditions. In modification, pigment follows the veins and the margin to 

 a much greater degree than in inheritance, where some characteristics are 

 wholly free from the influence of somatic structure, such as the spot q. 

 Of course this is just what should be expected. It is the opposite condi- 

 tion, where the hereditary and modificational changes are the same, sev- 

 eral cases of which have been shown in Part II. that calls for discussion. 



The most acceptable explanation is that the directing protoplasmic 

 elements in the developing somatic cells have so much in common witlrthe 

 protoplasmic elements in the germ-plasm that both are similarly affected. 

 If we assume this, some important corollaries follow. An environmental 

 influence may affect the soma and the germ-plasms simultaneously, so that 

 in the following generation there is the same effect as would have taken 

 place if there had been an inheritance of an acquired (somatogenic) char- 

 acter. Such phenomena as this are, I believe, not uncommon, not only in 

 the evolution of these beetles, but very generally. Indeed, recent neo- 

 Darwinian writings are making greater and greater concessions to this 

 view. The advocate of the inheritance of acquired (somatogenic) char- 

 acters must show the inheritance of a character which is incapable of 

 affecting the germ-plasm in the same way as it affects the soma. These are 

 particularly the kinetogenetic characters. The neo-Lamarckian may well 

 contend, however, that the admission that the germ-plasm is influenced 

 by the environment in such a way as to produce definite evolutionary 



