30 LABORATORY MOUSE 



ear families wavy tail appears to be absent. In some long-ear 

 stocks it is present. In the absence of complete genetic 

 analysis it is impossible to say whether the short-ear stocks 

 with straight tails lack the wavy tail through absence of a 

 gene or merely through lack of muscle tonus. If the wavy 

 tail is not another expression of the short-ear gene, then it 

 is linked with short ears as the researches of Gates and Keeler 

 have shown. The inheritance is probably that of a weakly 

 dominant unit-character. 



Flexed tail (/) (kinky?) 



In all cases the tail is permanently rigid over a varying portion of its 

 length, this stiffness being particularly conspicuous proximally. The 

 rigidity may be accompanied by permanent V-shaped, U-shaped, spiral, 

 etc., flexures. ... — Hunt and Permar, 1928. 



In some of the short-ear stocks bearing wavy tail a com- 

 plete right-angle flexure is found (11, 78, I4.8, 44)- The joint 

 is solidified by the fusion of vertebrae and the presence of an 

 osteosis. Sometimes two or three of these flexures may be 

 present in the same tail. This character may or may not 

 be that reported by Plate, 1910. Such heritable flexures are 

 found in long-ear stocks, but the identity or relationship of 

 these characters is uncertain. The inheritance of flexures has 

 been described by Hunt and Permar as a recessive which 

 sometimes fails to come to recognizable expression. 



Danforth, {27), in speaking of kinky tail (see Fig. 34) says: 



In these the caudal intestine instead of completely degenerating after 

 the sixteenth day as in normal individuals, persists until birth as small 

 remnants which become cystic or granular. Above these cysts the develop- 

 ing cartilages are thrown out of alignment and finally ankylose with each 

 other, forming permanent kinks. 



Posterior reduplication 



By selection there has been developed a strain of mice which give a 

 high percentage of young showing varying degrees of posterior reduplica- 

 tion. — Danforth, 1930. 



This character (see Fig. 32) ranges from Polydactyly to 

 completely formed additional posterior parts including legs, 

 genitalia, and alimentary tract {27). The inheritance of 

 the character is recessive and approximates the behavior 



