12 N. H. AGR. EXPERIMENT STATION. [Bulletin 160 



its development, can, however, produce a large-sized horn. A 

 glance at Tables I and II prepared from data obtained from cross- 

 ing various classes of horned and hornless sheep at this Station, 

 will show how this hypothesis feasibly explains all of the phenom- 

 ena of horns in sheep. Of course, the potency of somatic horn 

 production may also be raised in the male by the agency, perhaps, 

 of some material elaborated by the sex-gland, as the effects of 

 castration show; yet probably the female exerts a similar influence 

 although to a much less degree, which as yet cannot be proved 

 until our results of the unsexing of horned females are obtained. 

 However, it must be borne in mind that maleness can only act as 

 a stimulating influence, giving impetus to corporeal horn growth, 

 when the determiner for horn is present. The weak determiner, 

 H', upon the removal of this impetus may not be able to develop 

 whatever; but H will always produce horn in the soma, although 

 castration will lessen its potency, so that a smaller horn results. 

 It is obvious that the determiner for horn must always be present 

 in the germ plasm before a horn can appear. Where it is absent 

 in both sexes (the recessive condition) the offspring will under 

 all conditions be hornless; for two recessives can produce nothing 

 but the recessive condition. 



Morgan,* in a personal communication, after reviewing some 

 data I showed him, suggested that possibly the Merinos possessed 

 a special inhibitor to horn development which was absent in 

 other breeds; the assumption is tenable but unwieldy, and, 

 besides, presents the feature which is difficult to explain of how 

 the Merino alone should have an inhibitor, although virtually 

 analogous conditions as with the Merino obtain when horned 

 sheep are crossed with hornless, yet, under his hypothesis, devoid 

 of the inhibiting factor. It is more reasonable to presume that 

 the horn determiner of the Merino represents a lower or weakened 

 grade of that of the regular long horn as borne by the Dorset. 

 It is apparent, from an examination of the Dorset and Merino 

 crosses f especially the 1912 F 2 generation, that the horn of the 

 Dorset in itself is dominant to the Merino horn. This condition 

 then is very similar to that of human hair color, as worked 

 out by Davenport J (1909). In hair color the more intense or 

 the greater pigmentation is dominant to the less. The Dorset 

 horn clearly represents a more intense condition of horn than 

 that of the Merino, since the male horns are in most cases larger 

 and the females always bear long horns. 



The sporadic appearance of horns in Down rams and the loss 

 of horns in Merino rams can be readily explained. Many Down 

 ewes are simplex as to horns, but horns do not appear in the 

 soma owing to the counteracting influence of the double inhibitor. 



* Morsan, T. H., Columbia University. 



f See fables IX and XVI. 



j Davenport, Gertrude C., and C. B. "Heredity of Hair Color in Man." Amer. Nat., xliii, 193-211. 



