328 



Eeseaech in Animal Breeding. 



[July, 



inheritance may prove to be of economic importance for the 

 poultry breeder. Golds and silvers can be distinguished in the 

 downs of the newly hatched chicks. By mating hens belonging 

 to the silver class with cockerels belonging to the gold class, it is 

 possible to tell the sexes apart with certainty immediately they 

 hatch, and this is also true when barred hens are mated with 

 black cockerels. By making use of suitable crosses the breeder 

 of poultry for egg production can be sure of rearing nothing but 

 pullets thrQugh the earlier and more costly stages. If the method 

 were more generally followed, the poultry population of these 

 islands would consist of a far higher proportion of the more 

 valuable hen, and a markedly higher total production of eggs 

 for the same* expenditure of food and labour. 



During the course of our work we have kept a number of pure 

 breeds, and we have also made many crosses between them. A 

 point that has impressed us greatly is the superiority of the 

 first-cross birds as compared with the pure breeds. Under the 

 same conditions the hatching power has been distinctly better, the 

 chicks have been stronger, and mortality among them has been 

 markedly less than for the pure -breed birds. The results have 

 often been so striking that we feel it would be to the interest of 

 utility poultry breeders if more extended trials could be under- 

 taken. Carefully devised experiments of this kind might also 

 be expected to throw light upon some of the vexed problems 

 associated with inbreeding and crossbreeding. 



Our investigations into sex-linked heredity have served to 

 confirm and extend the earlier w^ork at Cambridge, w^here the 

 phenomenon was first discovered ; and w^e should state that even 

 ampler confirmation has been provided by other workers, notably 

 iii the United States. It is a phenomenon of great importance 

 to the breeder, for it undoubtedly plays a large part in the 

 heredity of animals with bisexual reproduction. Moreover the 

 understanding of it may prove to be of high economic value. 

 Professor Pearl in America has published an account of 

 some experiments which suggest that high fecundity in 

 poultry is transmitted on these lines. The highest grade of 

 laying hen owes this quahty to the possession of a definite 

 laying factor. But she is never pure for this factor, and, as it 

 is sex-linked in heredity, she transmits it only to her sons. 

 The high-grade layers therefore must get this factor from their 

 father, and the high prices paid to-day for the sons of hens with 

 a high egg record is evidence that the enlightened breeder is 

 already taking advantage of Pearl's experimental work. There 



