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



results constitutes a far-reaching compromise which goes far to justify 

 the faith he has placed in the role of environment. 



The fact that some characteristics are never inherited, but are always 

 mere modifications, and that others are wholly free from the influence of 

 modification, has a practical bearing to the systematist and to the breeder. 

 The systematist would do well to determine experimentally, where it is 

 feasible, which characteristics of those he deals with are especially sub- 

 ject to modification, by the differing influences of season and range. Such 

 will be his "poor" characters for species distinction and important ones 

 for subspecific distinctions. The breeder will find that characteristics espe- 

 cially subject to modification must be subjected to as uniform conditions as 

 possible, whereas this effort may be saved with other characteristics. 



The modifiability of Hippodamia convergens suggests that some of the 

 sub-species in this family might be merely ontogenetic in origin, but this is 

 doubtful, for all that I have brought to Cold Spring Harbor and bred there 

 have retained their characteristics. The variety moesta would naturally 

 be most subject to suspicion on this score, but it is found on the outskirts 

 of its own range in company with beetles which are even spotless and yet 

 without any loss of its typical character. Any rigorous attempt to modify 

 the germ-plasm, as accomplished by Tower (1906) in Leptinotarsa, requires 

 the subjection of large numbers under elaborately controlled conditions. 

 It is not surprising, therefore, that my attempts, which fell short of these 

 conditions, gave negative results when they did not result in death. Still, 

 I believe from the facts of variation and distribution that some such ger- 

 minal modifications as those in Leptinotarsa might be produced, but prob- 

 ably in a much smaller percentage of cases. Our interest here is primarily 

 in the imaginal coloration. Yet the far greater modifiability of the pupal 

 coloration, when the prepupa is exposed, is worthy of remark. The pupal 

 exuviae of Epialchna borealis varied from colorlessness, except in the spines 

 in the heat experiments, to a highly pigmented pattern of stripes and other 

 marks in the cold experiments described. 



DISTRIBUTION. 



If the view here entertained of the importance of the direct action of 

 the environment is correct, the task of unraveling the dispersal of a species 

 becomes more complicated. The criteria of Adams and others would be 

 less reliable in their application. The four criteria acceptable to Tower 

 (1906) of the considerable number that have been proposed by which the 

 center of dispersal can be located are as follows: 



(1) Location of greatest differentiation of a type (Adams). 



(2) Continuity and convergence of lines of dispersal (Adams). 



(3) Location of synthetic or closely related forms (Allen) . 



(4) In some cases, location of dominance or great abundance of indi- 

 viduals (Adams). 



