1 8 INHERITANCE OF COAT-PIGMENTS AND COAT-PATTERNS 



some force, the fact may be pointed out that regression does not occur in 

 the experiments made, and if regression were to occur at all, we should expect 

 it to occur and to be greatest in the early stages of a selection experiment. 

 The average grade of the offspring is sometimes greater, sometimes less, than 

 that of their parents, as we should expect if these deviations are purely the 

 result of chance. Table 4 (p. 36) shows the nature and amount of the 

 deviation following each selection made. No great importance attaches to 

 the exact amounts of deviation indicated in this table. For in computing 

 the parental averages all parents were weighted alike, but a better method 

 of procedure would have been to weight each parent in proportion to the 

 number of young which it produced. The general nature of the result 

 obtained is, however, not vitiated by the procedure followed; it serves to 

 show the absence of any uniform regression of either a plus or a minus nature. 



INDIVIDUAL SPOTS OF GUINEA-PIGS NOT UNIT CHARACTERS. 



In an earlier paper (Castle, : 05) the fact was pointed out by one of 

 us that in partial-albino guinea-pigs, as in other mammals, the pigmented 

 areas are not distributed without order over the body, but occur in regions 

 fairly definite. These regions in the guinea-pig consist of five paired "pig- 

 ment centers," dorso-lateral in position. To define their location more 

 accurately, they have been called the eye, ear, shoulder, side, and rump areas. 



The hypothesis was advanced (Castle, : 05, p. 45) that these several areas 

 might represent separately heritable unit characters, although experience 

 had clearly shown that, if such were the case, they were not inherited in 

 ordinary Mendelian fashion. To test this hypothesis more fully, we have 

 attempted to establish races of guinea-pigs which should possess certain of 

 the pigmented areas, but should lack others. For this purpose experiments 

 have been made with three different patterns of partial albinism, arbitrarily 

 chosen from those which occur among ordinary spotted guinea-pigs. These 

 are the Dutch-marked pattern (pi. 2, fig. 3), the head-spot pattern (pi. 2, fig. 2) 

 and the nose-spot pattern (pi. 2, fig. i). 



COLOR-PATTERNS SELECTED. 



In the Dutch -marked pattern, all the typical spots are present except the 

 shoulder spots. The absence of shoulder spots produces a white belt or 

 girdle round the body. Anterior to the girdle, eye and ear spots are present 

 and usually confluent on the same side of the head, but not across the median 

 plane. Posterior to the girdle, the large side spots and the small rump spots 

 are present and confluent over the back as well as lengthwise of the body, 

 forming a large blanket of pigment covering the whole posterior part of the 

 body, but not extending out upon the feet. This is the ideal "Dutch- 

 marked" type of the fancier. Occasionally it is fully realized, but more 

 often minor departures from the ideal occur, such as asymmetry of the 



