May, 1912.] INHERITANCE OF HORNS IN SHEEP. 15 



of Dorset rams and ewes were made every month from birth 

 until a fairly constant ratio was attained. It was discovered 

 that not until eighteen months of age did the horns reach a stage 

 of virtually perfect maturity beyond which appreciable fluctua- 

 tions in size no longer occurred in any great degree. The cir- 

 cumference at first expands to a greater extent than does the 

 length, consequently giving a less ratio. So far as we have been 

 able to judge from data at hand there seems to be no definite 

 rate of increase in growth, nor is it in any way comparable to the 

 growth of the body. When work of gathering this data was 

 commenced, Ave had in mind only the desire to be able to recog- 

 nize the period when variations in horn growth ceased. Since 

 then a new avenue of research has been opened up; namely, 

 variations in the rate of growth and the possibility of an inherit- 

 able tendency in this respect. 



At three months of age the rams possessed on an average a 

 ratio (length divided by circumference) of in round figures 2.00, 

 the ewes, 1.60; at six months the rams 2.60, the ewes 2.00; at one 

 year the rams 3.25, the ewes 2.50; and at eighteen months the 

 rams 3.40 and the ewes 2.70. The average ratio of a matured 

 horn, according to our measurements of forty-eight Dorset 

 Horn rams and ewes, was for the ram 3.44 and for the ewe 2.72. 

 This, I admit, does not represent altogether a fair average, since 

 only twenty-four individuals of each sex were included. In 

 order to establish a more exact average, measurements of several 

 hundred sheep should be made. However, in all instances the 

 ratios ran fairly uniformly, the difference between the highest 

 and the lowest in the ewes, which was the greatest, being .49 

 points. The difference between the ratios of the horns of the 

 rams and the ewes may be represented by a coefficient whereby 

 the ratio of the one may be expressed in terms of the other. In 

 this instance with the data we have at our disposal the coeffi- 

 cient would be 1.265. However, as I have already pointed out, 

 this factor, owing to the comparatively small number of meas- 

 urements of typical long horns we have been able to make, should 

 not be adjudged as absolute. We have used it only in making 

 rough comparisons. 



Where reciprocal crosses were made of a long horned sheep 

 (Dorset Horn) with a hornless sheep (Down), the females were 

 invariably polled and the males always possessed some indica- 

 tions of horn growth, varying all the way from minute scurs to 

 a medium-sized horn. The longest horn from such a cross had 

 a ratio of 2.86 and the shortest consisted of a scur with a ratio of 

 .32. Crosses of horned father and polled mother or vice versa 

 gave horns in the male offspring very similar in character or, at 

 least, no appreciable difference could be discerned. The right 

 and left horns of the Dorset Horn are almost invariably uniform, 



