UNIT-CHARACTERS (GENE MUTATIONS) 29 



Short ears (se) 



The mutation was found in a stock which originally came from the 

 Lathrop mouse farm and consists in a noticeable difference in size of ears. 

 — Lynch, 1921. 



As the name would indicate, this variety is characterized 

 by small ears (see Fig. 27). It is due to arrested development 

 of the auditory pinna {127). When both short-eared and 

 normal-eared animals are found in the same litter, one is 

 often able to distinguish the classes upon the fourteenth day 

 after birth. 



While the normal ear increases in length of pinna (87) 

 during the time from the fourteenth to the twenty-eighth 

 day from 0.71 to 1.16 cm. (63 per cent increase), the short 

 ear shows a gain from .60 to .76 cm. (27 per cent increase). 

 The skull shape of the short-eared mouse differs from that of 

 normals in that the nose is broader, while the cranium is 

 much narrower. The zygomatic arch is squarer than in the 

 normal. There is a certain amount of sterility noticeable 

 among short-ear animals. The gene underlying the develop- 

 ment of short ears is tightly linked with that for blue dilu- 

 tion and there is a relationship, not completely worked out, 

 between short ears and wavy tail. This latter relationship 

 will be touched upon under the heading of wavy tail. 



Wavy tail 



The behavior of this mutation is, like tailless, eccentric. — Gates, 1927. 



Some mice from birth show in the tail a series of zigzag 

 waves (61) bent in the horizontal plane. Such a condition is 

 commonly found in short-ear stocks. Wavy tail is purely 

 a neuromuscular condition (87), more extreme when the 

 animal is excited and disappearing in sickness, death, or 

 under anaesthesia. The loci of the flexures are constant 

 throughout life, as may be shown by tattooing a spot at the 

 point of each flexure. X-ray photographs reveal that the 

 caudal vertebrae are unaffected. The extended wavy tail is of 

 normal length. Snell maintains (159) that wavy tail is but a 

 second expression of the short-ear gene. Yet in some short- 



