IN RATS AND GUINEA-PIGS. 21 



table, accordingly, it will be observed, represents the summation of a large 

 amount of detailed information concerning the distribution of spots in off- 

 spring and parents, respectively. 



For convenience in comparing the categories of individuals one with 

 another, the entries in the tables are expressed in per cents, as well as in 

 numbers of cases observed. Thus in table 5, left-hand vertical column, 

 entries are made concerning the head-spot conditions of 49 young born of 

 parents both of which had two head spots. Of these 49 young, 42, or 85.7 

 per cent, had two head spots, as each of the parents had; 6, or 12.3 per cent, 

 had only one head spot; while i individual, or 2 per cent, had no head spots. 

 The other columns of the table are to be interpreted in a similar way. 



Glancing over the four divisions of table 5, which includes observations on 

 1 1 7 young, we notice that the offspring of parents both of which possess a 

 particular pair of spots (left-hand vertical column) possess that same pair 

 of spots in from 70 to 86 per cent of all cases. The agreement between 

 parents and offspring is greatest (85.7 per cent) in the case of head spots, 

 and least (70 per cent) in the case of side spots. 



From the last vertical column of table 5 we learn that when both parents 

 lack shoulder or side spots, 50 to 58 per cent of their young lack the corre- 

 sponding pair of spots entirely. 



These facts seem to indicate a rather strong degree of inheritance of par- 

 ticular spots upon the body of the guinea-pig; so we at first interpreted 

 them, but more extended observations limit this conclusion considerably. 



The four divisions of table 5 are combined in table 6, which accordingly 

 shows, for the body as a whole, to what extent particular spots are inherited 

 in the group of 117 individuals with which tables 5 and 6 deal. Inheritance 

 of paired spots is seen to be, on the average, measured by 78.8 per cent (left- 

 hand upper square, table 6) ; absence of paired spots is seen to be measured 

 in inheritance by 55 per cent (lower right-hand square, table 6). Further, 

 the fewer spots the parents have, the fewer their young have, as a glance at 

 the horizontal columns of table 6 will show. This is true not only of the 

 body as a whole (table 6), but also of its individual parts (table 5). Par- 

 ticular amounts of pigmentation are accordingly inherited quite strongly; 

 distribution of that pigment in certain of the typically pigmented areas, 

 rather than in others, is really not inherited, as we shall see, though such 

 is the impression first given by these tables. 



For the second group of individuals of Dutch-marked ancestry (mean 

 ancestral condition, Z?i), the observations concerning spot inheritance are 

 given in tables 7 and 8; for the third group (D 2 ), in tables 9 and 10; and for 

 the fourth group (#3), in tables n and 12. The numbers of individuals in 

 these several groups are 30, 178, and 136, respectively, making in the Dutch- 

 marked series as a whole 461 individuals observed. 



