110 CARNEGIE INSTITUTION OF WASHINGTON. 



Miss E. E. Jones, arose in the Bagg albino races. A white ventral patch 

 mutation was discovered by Miss Johnson and is being genetically investigated 

 by her. It appears to be a recessive. A mutation involving a white tip or 

 band on the tail is also being investigated and its relation to the ventral 

 patch is being considered. 



Heredity in Sheep. 

 The experiments on heredity of twinning in sheep were continued during 

 1922 and 1923, using as ram, in place of the member of a triplet set, a new ram, 

 the only lamb borne by his mother in 1920. In 1922, 11 lambs were born — 

 3 pairs of twins and 5 as single births — or an average of 1.38 per fertile ewe. 

 In 1923, 28 lambs were born, from the same sire, an average of 1.75 lambs per 

 fertile ewe. Thus using the same sire the proportion of multiple births was 

 greatly increased in the second year. This result can not be ascribed to the 

 greater fecundity of new ewes bred from in the second year; it indicates 

 rather improved vigor of the ram in his second year (a fairly obvious fact to 

 the casual observer) . The return to a fairly high fecundity, with nearly the 

 same stock, in the second as contrasted with the first year, shows the im- 

 portance for multiple births of a vigorous male. 



Genetics op the Thoroughbred Horse. 



At the request and expense of Mr. Walter J. Salmon, of New York City, 

 Dr. Laughlin has organized studies which have for their purpose the coordina- 

 tion of the performance and pedigree records of the Thoroughbred horse, and 

 the current breeding practices, by the aid of modern genetical knowledge and 

 methods of analysis. A library of very rare and valuable early pedigree and 

 performance records, purchased by Mr. Salmon, is used for this study. 

 There is perhaps no other collection of pedigree records extant for any plant 

 or animal which gives so complete and satisfactory performance data as the 

 speed-records of the Thoroughbred horse. This fact makes the work par- 

 ticularly promising, both for the elucidation of the practical breeding prin- 

 ciples of this particular breed of horse, and also (using the methods of pedigree 

 analysis) for the prediction of performance in offspring. The detailed 

 statistical work is being done by Messrs. Clyde E. Keeler, Pierre Hernandez, 

 and Misses Luella A. Smith and Alice Hellmer. 



As one of these special studies in horse genetics, Dr. Theophilus S. Painter, 

 of the University of Texas, made investigations at Cold Spring Harbor 

 during the summer of 1923, which resulted in a satisfactory and conclusive 

 count of the chromosome number in the horse. The diploid number is 

 demonstrated to be about 60, including a clean-cut X Y type of sex- 

 chromosome. 



Rabbits. 



Professor H. D. Fish, of the University of Pittsburgh, as associate of this 

 Department, has continued his researches on the extremely valuable strains 

 of rabbits which he is breeding. The maintenance of these strains encounters 

 certain difficulties arising from parasites, which at times have killed 95 per 

 cent of the offspring. Professor Fish has devised and installed partially self- 

 cleaning cages, and the mortality is now much reduced. 



New and improved grading scales have been introduced both for Dutch 

 and English rabbits, to indicate quantitatively the proportion of white pelage 



