Abstracts. - 309 



where 2 denotes summation of all values between the inclusive 

 limits indicated, and F-pn is a constant having the value set 

 forth in Table i. Fxn is of course the total area of the maxi- 

 mum brother X sister curve up to and including the n-j-i-th 

 generation. Studied by this unique measure the x\merican Jer- 

 sey Cattle are shown to be about 28 to 30 per cent as closely 

 inbred as the maximum possible inbreeding which could occur. 



THE SEX RATIO IN THE DOMESTIC FOWL.* 



The material dealt with is the sex ratio found in over 

 22,000 chicks representing the matings of eight years' work 

 by the writer. Data is presented to show that the normal sex 

 ratio found in chickens indicate an excess of females. This 

 excess of females is not a sporadic, but rather a regular phe- 

 nomon in the stock and conditions. The ratio in individual 

 families is shown to be approximately symmetrical about the 

 mean with high contact at both ends. These fitted curves make 

 possible some definite conclusions, thus out of every 1000 fam- 

 ilies of twenty birds one is expected containing twenty or more 

 pullets. 



This difference in males to females is not due to prenatal 

 mortality at least after the 10 days since of the dead embryoes 

 opened 927 w-ere males and 994 females. The conclusion is 

 justified that prenatal mortality is not differential in respect to 

 sex, and that in consequence the observed sex ratio at birth 

 is substantially the same as the initial zygotic sex ratio. 



AN INFESTATION OF POTATOES BY A MIDGE.f 



On October 25, 1913, potatoes were received from Roxie, 

 Maine, with the statement that they represented the condition 

 of an infested acre. The ti-ails contained numerous dipterous 

 larvae so different from any pest known to the writer that it 



*This paper is an abstract from a paper by Raymond Pearl, having 

 the same title and published in the Proceedings of the American Pliilo- 

 sophical Society, Vol. XVI, No. 5, 416-436. 



tThis is an abstract of a paper with the same title, by Edith M. 

 Patch, published in the Journal of Economic Entomology, Vol. 10, No. 

 5, 1917. 



