Heredity and sex . derthat the horns may develop fully, the male glands mustbe present and functional. In the Dorset, both sexes are horned, the horns of thefemales are lighter and smaller than the horns of theram (Fig. 68). In the castrated males the horns arelike those of the females. In this case we must sup-pose that the hereditary factor for horns suffices tocarry them to the point in development reached by thefemales. To carry them further the presence of the sexglands of the male is necessary. In the case of the hornless breeds I do not know ofany evidence from castration or ovariotomy.
Heredity and sex . derthat the horns may develop fully, the male glands mustbe present and functional. In the Dorset, both sexes are horned, the horns of thefemales are lighter and smaller than the horns of theram (Fig. 68). In the castrated males the horns arelike those of the females. In this case we must sup-pose that the hereditary factor for horns suffices tocarry them to the point in development reached by thefemales. To carry them further the presence of the sexglands of the male is necessary. In the case of the hornless breeds I do not know ofany evidence from castration or ovariotomy. We maysuppose, either that the factor for horns is absent; or, 136 HEREDITY AND SEX if present, some inhibitory factor must bring about sup-pression of the horns. The former assumption seemsmore probable, for, as I shall point out, certain experi-ments in heredity indicate that no inhibitor is presentin hornless breeds. The series is completed by cases like that ofthe eland and the reindeer. Both males and females. Fig. 69. — Fat-tailed hornless sheep (Ovisaries steatopyga persicci). have well-developed horns. In this case the hereditaryfactors suffice in themselves for the complete develop-ment of horns, for even after castration the horns de-velop. We have anticipated to some extent the conclusionsarrived at by breeding experiments in these races ofsheep. The best-known case is that of Wood, whocrossed horned Dorsets and hornless Suffolks. As THE EFFECTS OF CASTRATION 137 shown in the picture (Fig. 70) the sons had horns —the daughters lacked them. When these are inbred,their offspring are of four kinds, horned males, hornlessmales, horned females, hornless females. It seems probable that these four classes appear inthe following proportions: Horned $ Hornless $ Horned $ Hornless 3 1 1 3 The explanation that Bateson and Punnett offer forthis case is as follows : The germ-cells of the horned race
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Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectsex, bookyear1913
