SEX-LIMITED HEREUITY IN CERTAIN CROSSES. 147 



Two of the F2 hybrid males (of Hght brown color) were back-crossed with pure 

 St. alba (table 132) and with St. risoria (table 133). Both white and brown young 

 arose from both of these matings. With alba there were 9 white to 3 brown ;•= with 

 risoria, 4 white to 5 brown. The sex from none of the birds from the F. hybrid x 

 risoria mating is known; but from the F2 hybrid x alba mating the only brown 

 bird of known sex was a female, and the 2 known males were of white color.' 



BLOND RINGS AND BLOND-WHITE HYBRIDS CROSSED WITH JAPANESE RINGS. 



The Japanese ring-dove {St. douraca) is in most respects not greatly unlike the 

 blond ring {St. risoria) , but it is darker in color and the complexion of the newly 

 hatched young is decidedly darker. When the female douraca is mated to a male 

 risoria (table 134) the offspring present two colors; one is nearly as light as risoria 

 and the other nearly as dark as douraca. The lighter colored (like sire) birds are 

 ai:)parently all females and the darker forms (like dam) all males. 



Th(^ icf'iprocal cross gave again birds of two colors and apparently all of the 

 resulting females are of the darker color (like sire). The males, however, may be of 

 light or of dark color. The number of young obtained from this cross was too few 

 to throw much light upon the sex-ratio, or upon the proportions of the various colors. 



A risoria x douraca hybrid male mated to a blond ring gave (table 135) about 7 

 light and 5 dark offspring; 2 known males were dark and 1 was light; 3 of the 

 females were light and 1 was dark. Two of the young of this cross — Nos. F 1 and 

 F 2 — were mated and found to be fully fertile ; they hatched 2 dark and 1 light 

 colored young. One of these had a malformation of the upper mandible — 

 beak — which in these studies has been very frequently found among birds from 

 weak germs, germs of hybrid origin, and from inbreds. 



The cross of a risoria-alba hybrid with a douraca female yielded young which 

 approximate to the colors of the three parent species (table 136, pair 1). But it is 

 interesting to find here that 3 of the 6 young are "white," though white is "reces- 

 sive" (it is sex-limited) with both risoria and douraca, and though the offspring 

 here are but one-fourth cdba.>^ These 3 white young were all females, as was also a 

 mona-colored member of this fraternity; the two young which were nearly as dark 

 as the mother were males. 



The mating inter se of 2 pairs of these risoria-alba x douraca hybrids is of interest 

 in showing the lack of equivalence of the germs produced by the 2 pairs of brothers 

 and sisters from the same fraternity. Pair I (table 137) produced 3 dark and 4 

 white^ young, besides 5 eggs incapable of complete development. Pair II threw 

 no white birds in their total of 10 young. Here, however, 6 young were of the 

 lighter shade of risoria, and 4 were nearly as dark as douraca. The "develop- 



^ It is notable that the "brown" birds here arose in each instance from the first egg of the clutch, and that the 

 second egg in each of these same three cases developed into a "white" bird. 



' The further breeding of the white and blond rings was later turned over to Dr. II. M. Strong, who has already 

 reported his results (Biol. Bull., vol. 23, 1912, p. 293). 



* It is quite probable that the predominance of white offspring here is in part related to the fact that the sire 

 (li 1) had aJba as his mother. Both sire and dam, however, died of tuberculosis soon after these eggs were produced, 

 and prob.nbly cnnditinns (weakness) favored the production oi females (4 9 to 2cr). From another strong pair (3) 

 here were pioduc id :; inales to 2 females. These numbers, of course, are quite small; they are given for the sake of 

 compk'triic'ss.-- I'di HiR. 



9 Ilcic :if;:iiri I he "recessive white" appears in half (4 of 7) of the offspring, although these young are only one- 

 fourth SI. alba. — Editor. 



