72 INHERITANCE, FERTILITY, AND SEX IN PIGEONS. 



3 of the 4 infertile eggs belonged, moreover, to the very first clutch of the season, 

 while the fourth belonged to a last clutch of the season, this latter being at the 

 same time the last clutch laid during the life of a tubercular bird. The clutch- 

 mate to this infertile egg (table 40) produced a short-lived j'oung, which was 

 without trace of germ-glands. That the male parent then 10 years old also prob- 

 ably contributed to the weakness of these germs is attested by the result of the 

 tests made during the following year. These latter tests are recorded in table 41, 

 and show this 11-year-old bird to be much less fertile than when 3 to 8 years old.^ 



Three other matings of orienialis x alba have been presented earlier in another 

 connection (tables 25, 31, 35). The females in those crosses were mated to males 

 known to be weak in regard to fertility. In those cases many infertile eggs were 

 present, and most of the hatched birds did not show the long term of life exhibited 

 by the series of matings just described. Other features of the data for the orientalis- 

 alba crosses will be considered along with similar data for the reciprocal cross. 



Alba male x orientalis female. — The data of tables 42, 43, 44 (see also 23 and 30) 

 demonstrate that the increased length of life observed in the hybrids above described 

 is met with also in their reciprocals; the high degree of fertility observed there is 

 again equally evident here. In the first case to be noted (table 42) it is only during 

 the immaturit.y of the female parent, and at the extremes of the season, that there 

 is notable infertility.^ 



The relation of the two eggs of the clutch to the production of sex, and the 

 relation of season to sex, as it appears in the present data for the reciprocal crosses 

 of St. alba and T. orientalis, may now be considered. In the alba x orientalis 

 cross there occur 12 cases in which the two sexes arose from the two eggs of the 

 same clutch. In 10 of these the first egg gave rise to a male, the females being pro- 

 duced from the second of the clutch in these same 8 cases. In 2 cases the reverse 

 is true — ^the females here arose from the first and the males from the second of the 

 clutch. From the orientalis x alba cross there were 12 clutches which produced 

 both a male and a female. In 7 of these the first egg produced the male, the second 

 egg the female, and in 5 cases this order was reversed; 3 of these reversals, however, 

 came from a series (table 40) in which the female was probably not pure alba, and 

 we have elsewhere already noted, and will later again refer to it, that when the 

 female parent particularly is hybrid, the order of sexes from the two eggs of the 

 clutch is quite irregular." 



The data for these crosses which bear upon the "shifting of dominance "of sex 

 from spring to autumn, are perhaps not wholly conclusive. They do accord, 



' A similar result for the parents of this bird has been shown in t.able 19. 



' "See the young (No. 26, table 42) that failed to develop fully at the end of the season of 1908 — October. This 

 ;ood case, as it comes from a pair that have been very fertile." (R 16.) 



' The question of the relation of the order of the egg in the clutch to the production of sex in these and other 



1 has been, and is being, very thoroughly studied by the editor, who will presently report the findings in full. 

 In these studies it has become quite clear that the yolk-size of eggs (of pure species) is quite closely correlated with 

 the sex of the resulting offspring; and that yolk-size is usually correlated with the size of the whole egg. Whitman 

 learned that males predominate from the first egg of the clutch (see Chapters III and XIII, and he certainly had some 

 clear evidence that the total size of the first egg of the clutch w.as usually smaller than the second (see tables 174, 176, 

 177). The amount of data on this latter point (weights) is so small that it seems probable that some were in manu- 

 scripts which have never been avnilable to the editor. In our own studies the complete records on the egg-size of 

 incubated eggs indicates that in those cases where the usual order of the sexes (in the clutch) is reversed, the order 

 of yolk-size in these clutches was also reversed. In other words, maleness is associated with the smaller yolks, and 

 usually — though not always — the small yolk is found in the first egg of the clutch. 



