INHERITANCE IN HYDATINA SENTA 



I. VIABILITY OF THE RESTING EGGS AND THE SEX RATIO* 

 A. FRANKLIN SHULL 



The De'^artment of Zoology, University of Michigan 



TWO FIGURES 



CONTENTS 



Introduction 49 



Factors determining viability of eggs 50 



General account of the experiments 52 



Details of the experiments 53 



Viability in crosses and in inbreeding 55 



Effect of selection for low viability in a hybrid line 65 



Effect of selection for high viability in a hybrid line 69 



Effect of crossing on viability in two lines made different by selection. . 72 

 Effect of selection for high and low viability in the low viability series 



(repeatedly inbred) 74 



Effect of selection for high and low viability in the high viability series 



(repeatedly inbred) 76 



Results of the experiments 79 



Interpretation of results 83 



Nucleus and cytoplasm in heredity 86 



Summary 87 



Bibliography \ 89 



INTRODUCTION 



Several years ago in an attempt to effect crosses between 

 parthenogenetic lines of the rotifer Hydatina senta, it was found 

 that the proportion of fertilized eggs that would hatch varied 

 greatly in different lines. In one cross, only one egg in several 

 hundred hatched, although the batch of eggs was kept for weeks ; in 

 another, about one-eighth of the whole lot hatched. Since then 

 crosses have been made which resulted in a much higher pro- 

 portion of viable eggs, up to more than 50 per cent of viability. 



1 Contribution from the Zoological Laboratory of the University of Michigan. 



49 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 15, NO. 1 



