194 Experimental Zoology 
male of the A-series, her productiveness is not decreased. In 
other words, the A-male produces enough sperm to fertilize more 
eggs than produced by the females of the A-series, and as much 
as needed for the M- or N-series. The difference in productive- 
ness in the A- and the M- or N-series is due to a difference in the 
number of fertile eggs. 
The daughters of this union showed the same productiveness 
as the mothers of the M- and N-series; but none were sterile. 
Productiveness, therefore, in both cases dominates less produc- 
tiveness, unless, of course, the results are due to the cross itself 
bringing up the productiveness to the normal. 
, The grandchildren of both cross-series showed much varia- 
tion in their productiveness. Some were as unproductive as the 
A-series and contained sterile individuals. Others are as pro- 
ductive as the M- or N-series. It appears that low productive- 
ness may skip a generation and then reappear, as do characters 
that Mendelize. 
Selection of individuals of the same brood, that show high 
or low productiveness, gives positive results. The pairs taken 
from more productive broods are invariably more productive, as 
shown by the following figures : — 
PARENTAL Broop FILiaL Broop 
Lower productiveness 196 197 
Higher productiveness 232 239 
The annual cyclical rise and fall of productiveness, shown by 
the A-series in particular, but also by others, suggests the influ- 
ence of external factors, especially when transference to a warm 
chamber increased at once the productiveness. The experi- 
ments show, in fact, that temperature, upon which proper fer- 
mentation of the food depends, has a distinct influence; but 
independently of this, some families are characterized by high pro- 
ductiveness, others by low. ‘Improved conditions increase the 
productiveness of all . . . but the response is more prompt and 
vigorous on the part of a race normally high in productiveness.” 
