210 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Inspection of this table indicates that lugens is dominant over tau, 
for when the two forms are crossed, in Generation ILI., the offspring 
are apparently all of the lugens form, at least Standfuss does not 
mention the occurrence of any taus. The resulting fourth genera- 
tion hybrids, L in the table, but really L (T), when bred inter se, or 
when crossed with normal tau, produce, as we should expect, both lugens 
and tau forms. See Table III., crosses [1], [2], [3]. Likewise the fifth 
generation lugens, obtained by intercrossing lugens of the fourth genera- 
tion (cross [2]), produce when bred znter se both lugens and tau forms. 
See Table III., crosses [4], [5]. We have, then, convincing evidence that 
tau may be recessive (or latent) in lugens, but lugens is in no case shown 
to be latent in tau. Accordingly we have here a case of simple domi- 
nance of lugens over tau. The numerical proportions of lugens and tau 
in the crosses between those two forms are close to those demanded by 
the Mendelian principles of dominance and segregation. See Table IV., 
Generations III., IV. [1], and IV. [3]. But when hybrid lugens indi- 
viduals are bred ¢nter se ({2], [4], and [5]), considerable discrepancies 
occur between calculated and observed results. These discrepancies, I 
believe, arise from coupling —in the gametes produced by the hybrids — 
of the male character with the lngens character, and of the female char- 
acter with the tau character. This explanation accounts at the same time 
for the peculiar sex-distribution between lugens and tau forms observed 
in all the crosses. 
Suppose that in the germ-cells of every hybrid individual, D (R), the 
segregation of characters occurs in such a way that the male sea- 
character passes into the same gamete as the dominant (lugens) form-charac- 
ter. Then there will be produced only gametes D g@ and RQ. Ido 
not say that this is invariably so; indeed, it clearly is not so for any of 
the crosses in all cases. It occurs only in a certain number of cases in 
each cross, but this number is large enough materially to affect the 
result. The calculation, however, will be simplified if, for the time 
being, we suppose the segregation to occur in all possible cases among 
the gametes of hybrids. See Table IV. 
In Generation IV., crosses [1] and [3], a hybrid Zugens, D (R), is 
mated with a recessive wild tau, R. The two crosses are reciprocals, 
but the outcome is substantially the same in both, so that evidently 
whatever peculiarity is possessed by hybrid ova belongs also to hybrid 
spermatozoa. Suppose, as suggested, that it be coupling of the male 
character with the lugens character. Then we shall have gametes D ¢ 
and RQ furnished by the hybrid parent, and gametes R ff and R 9? 
