38 



EVOLUTION IN COLOR-PATTERN OF THE LADY-BEETLES. 



is clear that the end positions, that of no spot verms spot of normal size in 

 the one case, and lateral margin wholly incomplete versus normal in the 

 other case, are more stable conditions; otherwise we should probably have, 

 as a modal condition, a somewhat shorter pronotal dash and a narrower 

 margin, instead of the persistence of a variety in company with a parent 

 species. 



, 



FIG. 25. Offspring of 29.3, , exposed to inter- 

 mittent cold when a prepupa. 



FIG. 26. A new pattern, produced by inter- 

 mittent exposure to cold, which is not found 

 in nature. From Hippodamia conreryens. 



(</) 10 11 !.' j:j 14 15 16 IT 18 19 20 21 22 23 24 25 20 27 28 



(l>) 1 2 4 12 15 37' 35 20881000001 = 139 



(f) 7 12 28 35 44 20 3 1 = 150 



(eO 1 2 11 24 43 72 7'J 40 11 41000001 0=M-J 



FIG. 24. Variation of distance from the suture through spot 3 in Hippndti- 

 mia converyens at Fairfleld, Washington. 



(a) Distance from suture through spot 3. (b) Males. (<) Females. 

 (d) All individuals. 



Owing to the small number of extended pedigrees, the extent of domi- 

 nance and segregation in these beetles mast be examined in large part by 

 the comparison of the numbers in fraternities, only one parent or two 

 parents and one grandparent of which are known, with the theoretical 

 expectations under the several assumptions. In table 13 I have collected, 

 for convenience, the proportions to be expected under the various condi- 

 tions and assumptions. Thus, if a characteristic gives mixed broods when 

 interbred, it is not recessive, even if the allelomorph is more strongly inher- 

 ited. It is principally upon this criterion that so many of the pedigrees 

 fail to be simply Mendelian. 



Where all the spots are absent (table 15), in the parent, we find this 

 condition ordinarily in the offspring. In the progeny of the 12 females of 

 this kind which had mated in nature, we find that not infrequently a few 



