nOTES 



THE ODD EGG IN A CLUTCH. 



With reference to Mr. Riviere's note and the Rev. F. C. R. 

 Jourdain's footnote (Vol. IV., pp. 311-3) on the above subject, 

 last year, I had under observation a number of nests of the 

 House-Sparrow {Passer d. domesticus) built in the ventilators 

 of a large building in the country. 



I found that in every nest where there ^^'as an odd egg, it 

 was the last laid. I had not the opportunity to watch which 

 egg hatched first, so took a long series of eggs for reference, 

 and I also have a long series before me, taken at the same 

 place in 1903 for the same purpose. That the odd egg is 

 due to failure of colouring matter I have very great doubts, 

 because the odd egg is almost always marked quite differently, 

 in some cases being blotched while the other eggs are finely 

 speckled, and vice versa. Although the pale eggs show more 

 of the white ground-colour, the blotches are not weak in 

 pigment, and are what I should call, using a photographic 

 term, sharp — not washed-out or blurred. Looking at the 

 various clutches I find that A\'hat is the odd egg in one clutch 

 is the predominant one in another, and in some clutches the 

 last and odd egg is the darkest. 



I have seen it stated that the influence of the male of a pair 

 of birds cannot affect the colour of the egg laid by the female. 

 What I suggest, however, is that the colouring of the egg may 

 be affected through the male parent of the female having been 

 hatched from a clutch Avhere pale eggs were dominant. 



The regularity ^Yith which the odd egg occurs points rather 

 to some laAV at work, either Mendelian or another law somewhat 

 analogous to it, than to a mere absence of pigment. I should 

 mention that in some clutches of five there is no odd egg at 

 all. This may be caused through both the grandparents 

 being from a stock which laid pale eggs or vice versa, as I have 

 l)oth pale and dark clutches without an odd egg. 



On the other hand, I have clutches of six where there are 

 two " odd " eggs. That the odd egg is laid by the same female 

 and not deposited by another as I have seen suggested, is, I 

 think, proved in one clutch, in which all the eggs are of the 

 same peculiar shape, and in another in which all the eggs have 

 a fault in the shell — a small lump — in the same position in 

 each egg. 



