If we consider the male classes of table 11, we find that the smallest classes are eosin vermilion sable and wild type, which are the expected double cross-over classes if sable lies to the right of vermilion, as indicated by the crosses with eosin and with yellow. The classes which represent single crossing-over between eosin and vermilion are eosin vermilion, and sable, and those which represent single crossing-over between vermilion and sable are eosin and vermilion sable. These relations are seen in diagram II. w^e V s --+--------------------------------------------------+--------------+ X X --+--------------------------------------------------+--------------+ W v S DIAGRAM II.--The upper line represents an X chromosome, the lower line its mate. The cross connecting lines indicate crossing-over between pairs of factors. w^e s {Eosin sable. Non-cross-overs -------------------------- { v {Vermilion. w^e v {Eosin vermilion. Single cross-overs ------------+------------- { s {Sable. w {Eosin. -----------------------+-- { v s {Vermilion sable. w^e v s {Eosin vermilion sable. Double cross-overs ------------+----------+-- { {Wild-type. If we consider the female classes of table 11, we get information as to the cross-over value of eosin and sable, namely, 42 units. The male classes will be considered in connection with the cross that follows. The next experiment involves the same three gens which now enter in different relations. A double recessive, eosin vermilion (gray) female {39} was mated to (red red) sable males and gave 202 wild-type[5] females and 184 eosin vermilion males. Two F_1 pairs gave the results shown in table 12 (the four classes of females not being separated). TABLE 12.--_P_1 eosin vermilion F_1 wild-type [female] x F_1 eosin vermilion [male] [male]._