VARIATION IN DOMESTIC ANIMALS 463 



out must be struck from the records of observed mutations in domestic 

 animals. 



Another case in sheep which has no importance, perhaps, from a, 

 practical standpoint is reported from Norway. Wriedt writes that 

 among the old short-tailed sheep of certain districts in Norway, individuals 

 are found occasionally which possess very short ears. The short-ear 

 character is dominant and alternative in expression when contrasted 

 with the normal long-ear type. The records of one rather small flock 

 descended from a single short-eared ewe showed that during 20 years 

 not a single case of the production of short-eared offspring by long-eared 

 parents was observed. The fact of the simple character difference between 

 long and short ears is clearly established by these records, but whether the 

 short-ear type is the result of relatively frequent mutation may be a 

 matter of some doubt. Ritzman in fact has pointed out that the short- 

 ear character of native ewes when contrasted with the normal long-ear 

 type of such breeds as the Rambouillet, Southdown, and Shropshire 

 behaves as a simple character which exhibits alternative inheritance. 

 This confirms Wriedt's observation as to inheritance, but does not add 

 any evidence as to the origin of the short-ear type. 



The most frequently cited evidence of mutation in domestic cattle 

 is that of the polled character. Although this character is a simple 

 dominant the evidence of mutation or segregation in particular cases is 

 not always clear. Polled cattle have been known from ancient times and 

 they have not been entirely wanting in the foundation stock of any 

 modern breed. Within recent years the Polled Hereford and Polled 

 Durham breeds have been established by utilization of polled mutants 

 and by grading from horned Hereford and Shorthorn cattle respectively. 

 Within these breeds the so-called double standard animals, i.e., those 

 which are eligible to registry in the corresponding horned breed herdbooks 

 as well as in the polled records, presumably have all sprung from definite 

 mutations. However, of nine polled sports listed by Spillman all except 

 one were known to have near relatives that were polled. The two 

 Hereford bulls Wilson 126,523 and Variation 152,699 both apparently 

 came from horned ancestors. They were used by Boyd in establishing 

 a pure race of polled Herefords. They were both heterozygous, for in 

 matings with horned Herefords approximately half the offspring were 

 polled and half horned. A herd of pure-bred polled Holstein-Friesian 

 cattle has, also, been established in this country, but it appears to have 

 been established by utilization of normal polled animals of which there 

 are some representatives within the breed. Whatever the explanation 

 as to the origin of these rather numerous polled sports, however, there is 

 no question as to the correctness of Bateson's suggestion that the polled 

 condition is dependent upon a single dominant factor difference from 



