Abstracts. 289 



As would be expected from their derivation and as actu- 

 ally checks out to be the coefficients of variation do not change 

 within the age group for the cows which are retained in the 

 herd for longer or shorter periods. These facts show that the 

 cows which were kept in the herd as two year olds were all 

 equally likely to be kept in the herd until they became aged 

 cows as far as the milk production of these two year olds was 

 concerned. Generalizing this statement cows which were kept 

 in the herd at any given age were all equally likely to be kept 

 in the herd at any other age as far as the milk record of any 

 of those cows at the given age was concerned. This point re- 

 moves any possible objection to the accuracy of the correlations 

 for the milk productions at the various ages at least so far as 

 concerns the cows remaining in the herd on the basis of their 

 milk production being high. 



The correlation coefficients for the milk production of one 

 lactation with that of another lactation at another age range 

 from -f-0.2144zh.0919 to -j-0.7306rt.0284. The signs of these 

 correlation coefficients are all plus. The numerical values are 

 large enough to be significant. Each set of correlation coeffi- 

 cients for the milk production at a given age with the milk 

 productions at other ages in the cow's life do not deviate sig- 

 nificantly from a line taking a nearly constant value for each 

 age. The mean value for these correlation coefficients of milk 

 production of one lactation at any age with the milk production 

 of another lactation at another age is +°-535 2 - 



This mean value of the coefficient of correlation seems to 

 be generally applicable to milk production for on somewhat 

 similar data Gavin finds results which are comparable to these. 



These correlation coefficients are high for this kind of data 

 as may be seen from the fact that correlation coefficients of 

 similar nature for egg production range lower and have a lower 

 mean -I-0.4458 than do these correlation coefficients for milk 

 production. 



The magnitude of these correlation coefficients in compari- 

 son to those on egg production put in terms of the physiology 

 of the two sets of glands, mammary and ovary, that the mam- 

 mary gland works with more mechanical precision than does 

 the ovary. 



