624 



SCIENCE. 



[N. S. Vol. XXIV. No. 620. 



and caption) a marked preponderance of the 

 twelve-spots-free condition {A in Fig. 1) over 

 any other pattern type, but a much stronger 

 proportion of a certain one of the variant 

 types than of any other form of variant. This 

 second modal type is the one in which the 

 members of the middle pairs of spots are fused 

 on both wing-covers {B and G of Fig. 1). 

 The other important variants are middle spots 

 fused on either right or left wing-cover, pos- 

 terior spots fused on either or both right and 

 left wing-covers, and various longitudinal 

 fusings. Fig. 2 and its caption give the exact 

 data of the arrangement of this variability. 

 (The transverse fusing of the posterior spots 

 and all the longitudinal fusings are grouped 

 together as ' misc.') 



But note now Figs. 3, 4, 5, 6 and 7, with 

 their captions, giving the condition of this 

 color-pattern variation in the years 1901, 1902, 

 1904 and 1905, respectively. In all these cases 

 the variant B -{- G or middle-spots-fused type 

 is the predominating form. The following 

 table shows the relative frequencies of the 

 modal-pattern types in these successive years. 



If series of 1,000 really reveal the variation 

 conditions of the color pattern in the species 

 in these different years (and our check lots 

 show that they do) it is apparent from these 

 statistics that Diabrotica soror, in this par- 

 ticular locality has, in ten years, changed 

 from a form in which one pattern type was 

 the mode to one in which another is the mode. 

 And this change has been gradual and cu- 

 mulative; not made by a mutation or by dis- 

 continuous variation, i. e., discontinuous evolu- 

 tion. The two modes or predominant types 

 of pattern are connected to-day as they were 

 ten years ago by all degrees of gradations; 



* The second 1905 series was collected at a 

 distance of several miles from the locality on the 

 campus from which the other lots were taken. 



the variation, that is, is typically continuous 

 or ' Darwinian ' in type. Excluding then the 

 mutation or discontinuous variation explana- 

 tion of this species change there remain three 

 possible explanations of the change (on the 



Fig. 3. Frequency polygon of the variation in 

 elytra] pattern of 905 specimens of the Cali- 

 fornia flower beetle, Diabrotica soror, collected 

 on the Stanford University campus, October, 1901. 



basis of current theories of species-modifica- 

 tion) ; these are: (1) the change is simply 

 ontogenetic, determined for each generation 

 during its development by extrinsic influ- 

 ences; (2) the change is the result of natural 

 selection; and (3) the change is due to de- 

 terminate variation. 



The first explanation involves the assump- 

 tion that the pattern is not inherited as such, 

 but is acquired during the ontogeny of each 

 individual as a result of environmental influ- 

 ence; and it further has to assume a present 

 total environmental influence in this particu- 

 lar locality different from that in 1895 in the 



