34 SUMMARY OF CURRENT RESEARCHES RELATING TO 



but widely divergent at their caudal ends. The author refers to the two 

 rival theories of duplicity, that there are to start with two germinal 

 areas, or that one area undergoes partial or complete fission. A case of 

 ovum in ovo is described, the view taken being that a fragment of a 

 larger egg is ruptured off and enshelled, and then incorporated with the 

 next egg coming down. 



Inheritance in Hybrid Poultry.* — R. Pearl and F. M. Surface 

 have carried out a series of experiments in cross-breeding poultry, with 

 the general purpose of throwing light on the fundamental principles of 

 heredity. They publish an account of a detailed study of the reciprocal 

 crosses of the Cornish Indian Game and Barred Plymouth Rock breeds . 

 The percentage of fertility of eggs is found to be much higher when the 

 cross is made in one direction (B.P.R. $ x C.I.G. 9 ) than in the 

 reciprocal. The hatching quality of the fertile eggs is not greatly 

 different in the cross and its reciprocal. The hybrid matings in both 

 cases gave a much larger percentage of fertile eggs hatched than did the 

 pure matings. Study of the sex-ratios indicate that relatively more 

 males were produced among the hybrid chicks than among those from 

 pure matings, but the difference cannot be regarded as significant. The 

 mortality of the hybrid chicks from pure Cornish mothers was about the 

 same as that of the pure Cornish chicks ; and that of the hybrids from 

 Barred Rock mothers was about the same as of pure Barred Rock chicks. 

 The percentage mortality of all chicks from Cornish mothers was higher 

 than that of all chicks from Barred Rock mothers. Hybrid pullets from 

 Cornish mothers were relatively good layers, those from Barred Rock 

 mothers relatively poor. This result is discussed from the Mendelian 

 point of view. Shank and beak colour are inherited in a sex-limited 

 fashion. The down colour of the chicks in the female hybrids is 

 different from what it is in either of the two pure breeds crossed. 

 Dominance of pea-comb over single is found to be far from perfect. The 

 hybrids show a perfectly graded series of comb types from perfect pea 

 to the perfect single condition. In shape of body the hybrid males are 

 essentially like the pure Cornish Indian Game males. The hybrid 

 females are intermediate in shape of body between the females of the- 

 two pure breeds crossed. 



Inheritance of Colour-pattern in Hybrid Poultry.! — R, Pearl and 

 F. M. Surface discuss the barred or " cuckoo " colour pattern in hybrid 

 poultry. Barring is inherited in a sex-limited fashion ; the sex-limited 

 inheritance is equivalent to a phenomenon of segregation in the female 

 generation. The barred pattern is inherited as a unit character inde- 

 pendent of the pigment which fills the pattern, and " more intense " 

 pigmentation is dominant over " less intense " ; with the final result 

 that the actual somatic barring is less well-defined in the barred hybrids 

 than in their barred parents. The ground colour of the barring is 

 also different in the hybrids. There is no evidence of a blended in- 

 heritance of degrees of intensity of pigmentation. 



* Report Maine Agric. Exper. Stat (1910) 84 pp. (54 figs.). 

 t Arch. Entwick. Mech., xxx. (1910) pp. 45-61 (3 pis.). 



