21, BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
in the case of other crosses of a hybrid with a recessive form, namely, 
D(R)é + D(R) P+ Kh f +P Q, which is not the result obtained 
in this case. 
Hence to explain the exceptional results before us we must assume 
two exceptional occurrences, (1) a partial coupling, among the gametes 
of the hybrids, of the male sex-character with the dominant (lugens) 
form-character, (2) possession of sexual dominance by the gametes of 
the hybrid parent, when that parent is crossed with a recessive. But 
when two hybrids are intercrossed, as in Generation IV. [2] and Gen- 
eration V. [4] and [5], we should not expect to find sexual dominance 
possessed uniformly by the gametes of either parent, since both are 
hybrids. If, on the other hand, coupling occurs among al/ the gametes 
of both hybrid parents, only hybrid offspring will be produced and in 
the normal sex-proportion, approximately an equality. See Table IV. 
For each parent will produce only gametes D ¢ and R Q, and when 
opposite sex-characters meet, the zygote formed must always be D R. 
The result will be the same whether sexual dominance is possessed ex- 
clusively by the gametes of one parent, or is shared equally by those 
of both. The fact that in all of the three matings indicated a certain 
number of recessive offspring occurs, shows conclusively that coupling 
between the male character and the lugens character does noé occur in 
all possible cases. In Generation IV. [2], the total number of recessive 
offspring is even greater than it should be if no coupling occurred, and 
I am at a loss for an explanation of the discrepancy, unless one parent 
furnished considerably more than the theoretical number (one-half) of 
recessive gametes. But in the two similar crosses of Generation V., the 
total number of recessive offspring, on the supposition that no coupling 
occurs, is less than half the theoretical. In all three cases the se«- 
proportion among the offspring, both dominants and recessives, ap- 
proximates that which would result from chance combinations of gametes 
of two hybrid parents on the suppositions: (1) that there occurs a 
coupling of the male character with the lugens character and of the 
female with the tau character in approximately one-third of all cases, and 
(2) that when coupled gametes meet uncoupled ones in fertilization, the 
sex of the former always dominates in the zygote. On these two hypoth- 
eses, each hybrid parent will furnish gametes in the proportions 2 D @ 
+D9Q4+R 64 2B Q, of which one of the two D @'s and one of the 
two R 2 s will be coupled. If all possible matings occur and the coupled 
gametes are sexually dominant over uncoupled ones, the distribution of 
the offspring will be 8D g@:6D9:R4:3RQ. On this basis 
ee 
