134 JOHN C. PHILLIPS 



and the F2 lot 64. The results for 1912 are not, however, so 

 striking as those for 1911, but point in the same direction — to a 

 partial segregation of multiple size factors, or to a modification 

 of the gametes brought about by their association in Fi zygotes. 

 The increased variability in F2 is far greater in the male sex than 

 in the female. 



As a further index of size differences, external measurements 

 were taken on all the adult 1912 ducks. These were as follows: 

 Bill: exposed cuhnen. 



Tarsus: the tibio-tarsal measurement as used by the orni- 

 thologists. 

 Neck: from the anterior point of the breast bone to the tip 

 of the bill. The front end of the breast bone is a point 

 which can readily be felt. This measurement is easier 

 after rigor mortis has passed. 

 Length : tip of bill to end of tail feathers. 

 A summary of these measurements is given in table 2, for each 

 sex and generation. Among the eight pairs of coefficients of 

 variability obtained the F2 coefficient is greater than the Fi co- 

 efficient in five cases, the same in one case, and less than the Fi 

 in two cases. Accordingly greater variability of the F2 birds is 

 not very clearly shown in the measurements taken. 



GROWTH OF DUCKS 



In a recent paper Goldschmidt gives the result of some size 

 work in ducks. He does not deal with adult weights, but with a 

 coefficient of growth determined by dividing the weight at ten 

 weeks by the first or hatching weight. In this way he investigated 

 the early growth rate of several breeds. He obtained growth 

 figures for one lot of Fo Peking female mated with wild mallard 

 male, and records a great divergence, which he attributes partly 

 to segregation. It is to be remarked that Goldschmidt's wild 

 mallard race reached a weight of 1470 grams, which would sug- 

 gest that it might have been contaminated, for this weight is very 

 high. The average for my original stock of wild mallards is 

 1073 grams for the males, and 922 grams for the females, while 

 the autumn, or five month's weights for the offspring were 949 and 



