104 Experimental Zoology 
keeps on growing. At three months it is 6 tog cm. long. If 
shedding now takes place the animal never acquires longer hair; 
but animals that reach the age of four months without shedding 
their longest hairs may ultimately acquire hair 14 to 16 cm. long. 
It has been stated that long hair is recessive to short hair. 
When two long-haired individuals are mated, having hair of 
different lengths, the offspring have hair like that of the shorter- 
haired individual. In the next generation both long- and 
short-haired individuals occur, but the number of long-coated 
individuals exceeds the Mendelian expectation. 
A pure albino, long-haired, and rough-coated individual, was 
crossed with nine diffcrent pure, pigmented, short-haired, and 
smooth females. Twenty-nine young were produced, all pig- 
mented, short-haired, and rough-coated. Thus while two of 
the dominant characters come from the smooth-haired father, 
the third comes from the rough mother — the rough coat dis- 
sociating from the long hair to influence the arrangement of the 
short hair of the progeny. 
Castle and Forbes have recently extended Castle’s earlier 
experiments with short- and long-haired guinea pigs. When 
crossed the short hair dominates, but the hair of the hybrid is 
nearer the upper limit of variation of the pure, short-haired type, 
showing perhaps the influence of the other character. When 
the hybrids were inbred not only the two grandparental types 
reappeared, but a new intermediate type was present. This 
type contained individuals of all intermediate grades between 
the long- and short-haired types. It contained, first, individuals 
whose hair grew continuously from the age of twenty days on, 
but much more slowly than does the long hair, and shows a ten- 
dency to break off at lengths much less than that of the long hair. 
The long hairs were less numerous, as if some of the hairs only 
were continuous in growth, while the other hairs ceased to grow 
after a time. The alternative characters behaved somewhat 
like a mosaic. In other individuals the hair ceased to grow, 
z.e. was determinate in growth, but not until it had reached a 
length of 60 to80mm. These cases seemed to be a blend, but no 
