Effects of X-radiation on Pro- Duction of Mosaic Males and on Sex Ratio in Habro- Bracon. " in Press. Books Received

The above data take into account only the bisexual fraternities. In addition to these, 1,111 sisterless males were produced by 48 females which had been paired with x-rayed males. The mean number of progeny per female per vial for this group is 4.94 ± .1777. Since the matings of these females had been observed just as carefully as those of the controls (which produced practically no unisexual fraternities), and since the. mean number of progeny per female per vial for this group is significantly lower than that of either group of bisexual fraternities, whereas unisexual fraternities regularly include much larger numbers of individuals than do bisexual, we are justified in concluding that the absence of biparentals is not due to the lack of viable sperm, but rather to the presence of sperm capable of fertilizing the eggs and of preventing development. These "unisexual" fraternities thus are not comparable with unisexual fraternities from unmated females. They are initially bisexual, from which all the biparentals have been culled by the lethal effects of the sperm in fertilization. These data show clearly that we have to do, not with lethal action of x-rays on gametes, but with a true zygotic dominant lethal effect. Certain data reported by Raymond J. Greb4 tend to corroborate the conclusion reached from the above findings. While investigating the effects of x-radiation of mated females upon the rate of production of mosaic males in Habrobracon, Greb found that the number of sons per mother (in bisexual fraternities) was reduced slightly in the group of treated mated females, but that the percentage of females among the offspring was reduced significantly (20.8 per cent.) and that the total number of offspring per mother was also significantly lowered (37.32 per cent.). The points to be noted here are: first, that while the number of females was considerably lowered among the progeny of treated, the number of males produced did not increase to the extent of preserving the same average number of progeny per mother as that for the controls; and, second, that although this lowering of the general fecundity among the treated may not stand alone as conclusive evidence for the production of dominant lethals (because of the uncertainty as to the extent to which the direct effects of x-radiation on the eggs contributed to this diminished fecundity), they are in accord with the results obtained from the investigation in which the males alone were x-rayed. M. F. STANCATI UNIVERSITY OF PITTSBURGH