♂ 8000, a wild gray rat caught in Cambridge, Mass., October, 1908.
♀ 6176, a black hooded rat of grade -1¾ which was mated with ♂ 8000.
♂ 8021 and ♂ 8018, _F_₁ offspring of the pair just described, ♂ 8000 and
♀ 6176. ♂ 8021 is of grade +4¾, with considerable white below. Notice
also his white legs and compare with those of his father. ♂ 8018 is of
grade +5½. Notice white areas on belly and front legs.
8075-8078, four F₂ progeny (grandchildren) of ♂ 8000 and ♀ 6176. 8075
is black hooded, grade ¾; 8076 is gray, +4¼; 8077 is gray, +4; 8078 is
black, +5½.
[Illustration: PLATE 2]