302 THE AMERICAN NATURALIST [Vol. LVI 



NUMBERS OF RATS PER LITTER 



from treated parents gave 33.3 + 8.2 per cent, more lit- 

 ters than their controls, and the untreated rats from un- 

 treated parents and treated grandparents produced 55.6 

 + 8.4 per cent, more litters than their controls (see Fig. 

 5). All of these differences are, without doubt, statisti- 

 cally significant. 



Di^rn^'sinii.- -Two generations of treatment made less 

 diflVicrn-t^ ill hiitiiIkt of litters than a single generation 

 of Irt'atnit rit, and two untreated generations following 



