No. 570] 



SPECIES-BUILDING 



335 



may readily be bred. When one of these males is mated 

 with a lacticolor female, there is produced in captivity a 

 pure lacticolor strain. If lacticolor males and females 

 should be segregated and allowed to breed together until 

 they have become as abundant as the typical form, this 

 ease would then resemble that of the Colorado lady beetles 

 of the genus Adalia, described above, in that it would con- 

 sist of different types maintaining their identity while 

 freely interbreeding with complete fertility. The 

 Abraxas complex differs from the Adalia species-cluster, 

 however, in the occurrence of sex-linkage in the inheri- 

 tance of the lacticolor variety, whereas in Adalia the 

 factors for the different color patterns apparently are 

 distributed in the gametogenesis of a heterozygous indi- 

 vidual without sex-linkage, freely and at random. 



A more advanced stage in evolution is that represented 

 by the Basilar chia species-cluster, in which partial steril- 

 ity between the viceroy and the two purple species, over 

 the faunal areas of which its own overlaps, and the differ- 

 ence in geographical distribution between the banded 

 purple and red-spotted purple, keep the three elements 

 apart. 



By easy stages we may in imagination pass on to 

 groups composed of closely allied species which sterility 

 and local segregation completely separate from one 

 another, groups that probably have arisen from a poly- 

 morphic species that has broken up into its constituent 

 parts, and thus given rise to new elementary species. 



The dimorphism of Colias differs from that of Abraxas 

 in that the color of the rarer type of female can not be 

 transferred in the ordinary course of breeding, without 

 further mutation, to the male. It is a sex-limited char- 

 acter, like the female color pattern in Colias, (i. e., a wide 

 dark border broken with spots) and not sex-linked like 

 the variety lacticolor of Abraxas. 



The white female of Colias is regularly heterozygous 

 for color. She produces as many white daughters as 



