232 OSCAR RIDDLE 



hybrids. In only one case of the thirty-six clutches listed — 

 one in which the difference in egg weight was only 13.9 per cent — 

 did the difference in egg weight fail to show which egg contained 

 the larger yolk. This failure, moreover, concerns the first pair 

 of eggs laid during the life of the bird, and this has long since 

 been observed to be a clutch in which the usual order, both of 

 sex delivery and of yolk size, is more often disturbed or reversed. 

 It may be incidentally noted that the first clutch produced after 

 prolonged reproductive rest is similarly disposed — even in pure 

 species — to supply a large yolk to the first egg and a small one to 

 the second egg, and to reverse the normal order of the resulting 

 sexes in the same sense. 



Table 8 will show that the other twin-producing egg, that of 

 hybrid female No. 60, was an extraordinarily large egg when 

 compared with the extraordinarily large eggs produced by any 

 and all of our hybrids of similar or related kinds. Only three 

 eggs of the fifty-two pairs from all similar sources equaled it 

 in size. The data of the table leave no doubt that this twin- 

 producing egg contained a yolk of unusually large size. 



The effects of hybridity in the female on the regularity of 

 delivery of larger eggs and yolks in second eggs of the clutch (as 

 indicated by the segment of data contained in the several tables) 

 may be summarized as follows : 



[Eees 2nd larger, 20; smaller, 0\ ,, , , „. 

 P"^^ St. nsor.a lYofks, 2nd larger! 7 i smaller, o) ^^^'^^^ '^ 



, r,-, • , 1- [Eggs, 2nd larger, 6; smaller, 0\ , , , 

 Pure St. alba and T. onentahs. . ^%' ,. ^t' ' ^.. . (table 



\ Yolks, 2nd larger, 2; smaller, 



9) 



■D- ■ ^u X. u -A /Eggs, 2nd larger, 48; smaller, 4l , 



Risona-alba hybrids ^Yolks, 2nd larger, 48; smaller, 4J ^^^'^^^ ^^ 



,,. ,, , , •, (Eggs, 2nd larger, 14; smaller, 4\ . , , . 



Miscellaneous hybrids [^%^^^ ^nd larger, 11; smaller, s/ ^'^^^' ^^^ 



. /Eggs, 2nd larger, 2; smaller, 2\ , , . 



Common pigeons ^Yolks, 2nd larger, 1; smaller, s/ ^^""^^^ ^^^ 



Alba-orientalis hybrids (generic /Eggs, 2nd larger, 27; smaller, 35| /^^^j^jg jj) 

 hybrids) \ Yolks, 2nd larger, 26; smaller, 34/ 



