8 



HEREDITY OF HAIR-LENGTH IN GUINEA-PIGS. 



hair attain a length of 200 mm. As the longest hairs are shed, new ones 

 are found to be growing up to take their places, but there is usually a period, 

 after shedding sets in and before the second-growth hairs are fully devel- 

 oped, when the maximum coat length shows a decided falling off. This 

 is indicated in D, Fig. 2, as occurring at about the age of two hundred and 

 and fifty days. The type of hair growth found in class D may be called 

 indeterminate or continuous; that of class A, determinate. 



Kge in days 



Age da /S 



FIG. 2. 



Our original stock of short-haired guinea-pigs showed considerable 

 variation in maximal hair-lengths, ranging from 35 to 50 mm., but all of 

 the determinate type of growth (classes A and B, Fig. 2). The great 

 majority of them would probably have fallen in class B, but we can not be 

 sure of this, as many of the animals were no longer available for record 

 when we began making hair-measurements systematically. The hair-lengths 

 recorded for class A are certainly exceptionally short, even for animals of 

 determinate hair growth. 



