GENE AND CHROMOSOME MUTATIONS 237 



sion of shedding, hair tending to thin out all over. Also hair persists on 

 feet as late as seventh week instead of falling out at 2 weeks as in hrhr mice. 

 At about 3 weeks hf^hr''^ mice begin to show a wrinkling of the skin which 

 becomes very pronounced in old animals, giving ''rhinoceros" appearance. 

 Recessive to hr. Howard, 1940, J. Hered. 31: 467-470. 



hy-i hydrocephalus- 1. — The lateral and third ventricles and the foramina 

 of Monroe are distended with accumulated fluid. The aqueduct of Sylvius 

 is occluded. The swelling of the head may be detectable at birth but usually 

 does not become noticable until a week or two later. Affected mice become 

 grotesque in appearance, lack coordination and finally die during the third 

 or fourth week of postnatal life. Clark, 1934, Anat. Rec. 58: 225-233. 

 Clark, 1935, Proc. Nat. Acad. Sc. 21: 150-152. 



hy-2 hydrocephalus-2. — The ventricles of the brain are distended with 

 fluid and the skull enlarged. These brain defects are detectable at least as 

 early as 4 days. Growth is much retarded and there is a high mortality 

 particularly during the first week. Adults are sterile and usually about one 

 half normal size, though the size varies considerably. Zimmermann, 1933, 

 Z. ind. Abst.-u. Vererb. 64: 176-180. 



/;/ leaden. — Phenotypically almost indistinguishable from d. Murray, 

 1933, Am. Nat. 67: 278-283. 



?ny myeleneephalic blebs. — ^Large blisters tilled with clear fluid appear 

 on the back of 7-8 mm. embryos and move toward the extremities where 

 they tend to cause bleeding and various foot and eye defects that persist 

 in the adult mouse. The expression of the gene in the adult mouse, at least, 

 appears to be subject to frequent normal overlaps. Bonnevie, 1934, J. 

 Exp. Zool. 67: 443-520. 



A naked. — Chromosome 6. Linked with Ca (which see). NN mice are 

 almost completely hairless from birth; vibrissae absent. Sterile, except 

 that occasional males show low degree of fertility. In Nn mice the coat 

 appears almost normal up to 14 days, though usually a little short and dull; 

 thereafter the hairs break off before attaining normal length, so that parts 

 of the skin are naked, other parts covered by hair. Fertility of heterozygotes 

 is normal. David, 1932, Z. Zellforsch. u. mikr. Anat. 14: 616-719. 



p pink-eye. — Chromosome i (see C). Eyes pink, coat much lightened, 

 tending towards brown or yellow. Recognizable at birth by lack of pigment 

 in the eye. Little, 1913, Carnegie Instn. Wash. Pub. No. 179: 11-102. 



pa pallid (pink-eye-2). — Chromosome 5 (see A). Rather similar pheno- 

 typically to p but causes more extreme dilution of coat color. Eyes pink, 

 unpigmented. Roberts, 193 1, Science 74: 569. 



