206 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
1. RevativE INFERTILITY OF CERTAIN COMBINATIONS OF GAMETES. 
Tutt (98) reports that in crosses between two nearly related species 
of Lepidoptera, Tephrosia bistorta and T. crepuscularia, it has been 
found that when bistorta is the male parent, the hybrid offspring show 
a normal distribution as to sex, a slight excess of males. See crosses 
[1] and [2] in Table I. But in the reciprocal cross, with crepuscularia 
(or its dark aberration, delamerensis) as the male parent, the offspring 
are practically all males. See Table I., crosses [3] and [4]. 
TABLE I. 
Sexz-proportions among two generations of hybrid offspring of Tephrosia bistorta (B) 
X T. crepuscularia (C) or the dark aberration of the latter, delamerensis (D). 
[Statistics of Tutt (98). ] 
Pi ko Bo De Cs Be De 
ee hg Nai aaa 
| fal | ar | 
3 arg 9 d ge 9 
0 118 1 
92 75 OY 6: 
\ 
ate. 
Pe LS 0 5] 
| 
d e 
Hybrid female offspring of bistorta g X delamerensis % (cross [2], 
Table I.) when crossed with crepuscularia g gave (cross [6], Table I.) 
a large excess of males, as we should expect on the Mendelian hypothesis 
that the hybrid furnishes in equal numbers gametes having the pure 
character of either parent race. For we should expect the combination 
of pure delamerensis with crepuscularia gametes, which would occur in 
half the total cases, to yield offspring having the normal sex-proportion, 
a slight excess of males (compare cross [1], Table I.) ; but pure bistorta 
ova fertilized by crepuscularia sperm should yield only male offspring 
(compare cross [3], Table I.). Accordingly the result to be expected is 
3+ g: 19; the observed result is 38 g: 11 9. 
To explain the peculiar sex-distribution observed in these crosses, we 
may make two simple hypotheses, which, I believe, are warranted by 
the facts observed. (1) The sex-character borne by a listorta (B) gamete 
