28 LABORATORY MOUSE 



''silver-fawn" color. The blue-dilute condition consists in a 

 reduction in number of pigment granules in addition to a 

 clumping of these granules. There is no noticeable change 

 in iris pigmentation, but the cleared retina is lighter in color 

 than that of the normal black eye. 



Naked (N) (dominant hairless, "half-naked") 



The whole bodies of these three little creatures were completely naked, 

 as destitute of hair and as fair as a child's cheek. There was nothing 

 peculiar about the snout, whiskers, ears, lower half of the legs and tail: 

 all of which had hair of the usual length and colour. — Gordon, 1850. 



Naked (see Fig. 28) is a peculiar physiological condition of 

 the skin causing alternate waves of falling hair and regenera- 

 tion (66). These waves (108) pass from head to tail, three 

 or four waves being visible at a given time. Vibrissa? are 

 present as well as the short hairs upon the tail. The 

 homozygous naked (see Fig. 30) is devoid of tail hair and 

 vibrissa?, and is semi-lethal. Animals of this constitution are 

 difficult to raise and are usually sterile. These mice have the 

 skin normal in texture and general appearance. The genetics 

 of this variation as a dominant unit-character was first 

 worked out by Lebedinsky and Dauvart (1927). 



Recessive hairless (hr) (rhinocerus?) (151, 3, 14) 



In November, 1924, I received from a gentleman in North London, a 

 pair of pink, smooth-skinned, hairless mice, which he had captured in his 

 aviary. — Brooke, 19 L 26. 



This type of hairless animal (see Fig. 29) has no tail hair 

 but retains vibrissa? (12, 130, 60). It has wrinkled, dry skin 

 of at least three times normal thickness. A few aberrant 

 hairs coil about within and even under the skin. Such hairs 

 may be seen in the dried skin, which is rendered transparent 

 by the natural oil contained within it. The skin is filled with 

 granular cysts. Hairless females are usually sterile and the 

 stock is maintained by breeding hairless males to their heter- 

 ozygous sisters. The gene for hairless (hr) is linked with 

 piebald (s). 



