May, 1912.] INHERITANCE OF HORNS IN SHEEP. 17 



although in six per cent, of cases examined a very slight differ- 

 ence did exist. 



Matings between hornless sheep invariably produce hornless 

 females, and males that are either hornless or possess intermediate 

 (simplex) horns. The hornless females may be pure or simplex, 

 which selective breeding alone will show, unless their lineage for 

 several generations is known. The hornless males cannot re- 

 produce a horn. 



The experience of practical breeders, as I have stated here- 

 tofore, provides proof of this, and in our own breeding oper- 

 ations hornless males bred upon recognizedly pure hornless 

 ewes have never produced in the male offspring the slightest 

 semblance of a horn. The horned males of this cross are clearly 

 simplex. 



The knobs of Merino ewes are not mensurable. In general 

 they are most variable as to size. Sometimes they can scarcely 

 be discerned, but can always be felt by a careful observer. They 

 may simply fill the depression which normally exists in hornless 

 ewes at the horn pits or they may protrude as much as an inch 

 and a half beyond the skull. So far as our knowledge extends 

 the knob condition exists only in Merino sheep and will be present 

 in females, without producing a scur or horn, through successive 

 generations. However, in some instances, as I have already 

 mentioned, the knob may disrupt the skin, producing a scab- 

 like horn or a scur. 



Our belief that the knob represents the duplex condition of 

 the Merino horn (H'H') is based on the data contained in Tables 

 VIII and IX. These records show that when crosses with other 

 breeds are made, the knobs disappear, the Fi female offspring 

 possessing either an entire absence or a long horn according to 

 the nature of the mating. When a ewe bearing the knob char- 

 acter is crossed with a long horned ram other than a Merino, 

 the offspring, both rams and ewes, possess long horns. We have 

 had no exception as yet to this rule; our knowledge, however, 

 comprehends but a few examples. The length of the horns of 

 the Fi offspring, although the ratio of length to circumference is 

 somewhat less than that for the long horns of the Dorsets, clearly 

 entitles their inclusion in the long horn class. This patently 

 proves that the Merino bearing a knob must possess two horn 

 determiners in her germ plasm; otherwise, we should have some 

 hornless females and males with simplex horns. It further 

 proves that the potent horn determiner of the Dorset is not offset 

 by the weakness of the Merino determiner but rather strengthens 

 it, for the two together are capable of producing a heavy horn, 

 almost as large as the pure Dorset horn. The offspring from 

 matings between a hornless ram and a ewe bearing knobs are in 

 every respect similar to those of a hornless and a long horned 



