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 : — 



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 famihes 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." 



