30 



EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



The variation of the number of spots is shown in table 7. At Palo Alto 

 (data from Kellogg and Bell, 1904) and at Cold Spring Harbor the polygons 

 are not regular, but show a normal condition of 6 spots, with a scattering 

 few having aberrant numbers. I have grouped 25 specimens, said by 

 Kellogg and Bell to have 1 or more extra spots on one or both sides, with 

 those having 6 spots, because the irregular position of these spots and my 

 experience with living specimens makes me believe that such spots are 

 nearly always, except when at e and q, of ontogenetic origin. The poly- 



I"n;. 17. Relative frequency of loss 

 of the several spots in the iienus 

 ft. Broken line, col- 

 lection of KelloKK and Hell from 

 Palo Alto, California; entire line, 

 collection from Kamiack Butte, 

 Washington. 



gon for Kamiack Butte might have shown about 0. 5 per cent, with a seventh 

 spot e, but I have not put these in, because no accurate account can be 

 made of spot e, as it may be entirely covered with pigment from spot 3 and 

 the scutellar mark. Now, in contrast to the condition at Palo Alto and 

 Cold Spring Harbor, we have at Kamiack Butte a polygon not greatly un- 

 like the half-Galton curves found in some petal-counts. Yet the real nature 

 of the variation in the three cases must be the same. Such an instance 

 shows us that the distinction between continuous aud discontinuous varia- 

 tion is not a sharp one. 



The order in which the spots disappear has proved to be a matter of great 

 interest. I have tabulated the data given by Kellogg and Bell (1904) 

 Palo Alto, California, in table 8, and fig. 17 (broken line), but have 

 numbered the spots according to Weise. There is no very pronounced 

 order of disappearance here, the most prominent feature being the persist- 

 ence of spot 2. But at Kamiack Butte (table 8, fig. 17) , a very different 

 condition prevails. Here spot 1 exhibits a strong tendency towards disap- 

 pearance, and this happens in spite of the fact that it is in company with 

 several varieties having spot 1 unusually large and in some cases confluent 

 with spot 3. Spot 6 follows it in order of non-development and then spot 

 2, which at Palo Alto was most persistent. It is evident, then, that not 

 only is there a definite order, but that this diff ers from place to place. The 



