170 Heredity of Horns [cil x 



horns are well developed in both sexes. These he crossed 

 reciprocally with Suffolks, a breed without horns in either 

 rams or ewes. The F^ male lambs all developed horns of 

 fair size, but the F^ ewes remained hornless. The horned 

 character may therefore be described as dominant in males 

 and recessive in females (Fig. 20). 



The 7^^ generation bred from these consisted of all the 

 four types, horned and hornless males, horned and hornless 

 females. The experiment was not carried out on a scale 

 sufficient to justify a statement that the numbers are simply 



Males Females 



3 horned : i hornless i horned : 3 hornless 



but so far as the evidence went these simple ratios seem to 

 be followed. (For diagram of such a descent see Fig. 33.) 



Subsequent experiment has confirmed the conclusion 

 indicated by these facts, namely that horned ewes in F, are 

 pure for the presence of horns, and that hornless rams in F^ 

 are pure for the absence of horns. 



In order therefore that the female may possess horns, 

 she must be homozygous in that character. The factor for 

 hornedness must come in from both sides of the parentage. 

 Conversely, in order that the male should be hornless, he 

 must receive the deficiency from both sides of his parent- 

 age. A case that may be compared with this has been 

 observed in regard to the descent of wing-development in 

 a cross between two species of moths of which the one 

 Boarmia {Biston) hirtaria has a winged female, while the 

 other, Boarmia {Biston) pomonaria, has a wingless female. 

 Oberthur"^ crossed these two species and obtained F^ males 

 all with fully developed wings and four females with wings 

 only half-formed, in a condition thus intermediate between 



as horned cattle are concerned. The heterozygote is either quite hornless, 

 or has only small loose horny lumps — "■ scurs " as they are called in the north. 



As to the descent in goats I have no thoroughly adequate evidence. 

 The Rev. E. P. Boys-Smith has kindly given me particulars of many 

 matings which he has made, but the details are complex and I have not 

 been able to extract a consistent scheme from them. There is probably 

 some intricacy due to gametic coupling comparable with that described in 

 the next section, or perhaps to sex-limitation. 



♦ Bull. Soc. Ent. Frafice^ 1897, p. 256. 



