140 CARNEGIE INSTITUTION OF WASHINGTON. 



between the X and Y chromosomes in the heterozygous sex and, in the 

 case of non-disjunction, sterihty, which is also, as yet, unobserved. 



To explain these cases, therefore, it is suggested that in certain rare 

 individuals factorial changes from one allelomorph to another take 

 place as follows: 



In cats, from sex-linked factor Y, for the restriction of black pig- 

 ment, to factor y, for the extension of black pigment to these regions. 



In doves, from sex-linked factor w, for white plumage, to factor W, 

 for colored plumage. 



In canaries, from sex-linked factor p, for pink eye-color, to factor 

 P, for dark eye-color. 



To explain the second category, it is suggested that non-disjunction 

 of the X chromosome, resulting in certain "males" which are X 

 instead of XY in formula, is involved. Sterile tortoise-shell male 

 cats are supposed to be animals of the constitution X, showing a 

 peculiar mosaic distribution of black and yellow color. Similarly, the 

 still rare fertile tortoise-shell males are considered as the result of sec- 

 ondary non-disjunction. These hypotheses are tentative and have 

 been advanced by Dr. Little for consideration and experimental test. 



HEREDITY IN SHEEP, MICE, AND POULTRY. 



The experiments on heredity of twinning and multinippling in sheep 

 were continued at the station. There were 30 lambs bom from 17 

 mothers, being a proportion of 1.8 lambs per mother, as contrasted 

 with 1.6 for 1917 and 2.2 for 1916. The cooperative sheep experi- 

 ment with the New Hampshire Sheep Experiment Station is being 

 continued. 



Progress is being made with the poultry strains. During the year 

 109 chicks were hatched, mostly of the New Buff and Silky strains. 



Dr. C. C. Little, who has been in part assisted by Mr. L. C. Strong, 

 a graduate of Columbia University, has worked on an operative 

 technique for ovarian transplantation in 1-day and 2-day old mice, 

 in a series of over 300 operations. From this material it is hoped that 

 evidence relating to the effect of the foster-mother on heredity of sus- 

 ceptibility to tumors, spotting, size, etc., will be secured. Mr. Strong's 

 work was chiefly making operations upon older mice, with the view of 

 continuing his work at Columbia University. 



Mr. Reginald G. Harris, cooperating with Dr. Little, has measured 

 skull and size inheritance of crosses in mice. Results of this will be 

 included in the paper on the characteristics of mice which is now being 

 prepared for publication. Dr. Little has also collected a series of over 

 600 mice in order to study the effect of age of transplantation to 

 susceptibility to tumor. These animals are now under observation. 

 Dr. Little proposes to continue this work as a control to the ovarian 



