Vol. XXIV. December, 1912. No. i. 



BIOLOGICAL BULLETIN 



THE INFLUENCE OF INBREEDING ON VIGOR IN 



HYDATINA SENTA. 1 



A. FRANKLIN SHULL, 

 DEPARTMENT OF ZOOLOGY, UNIVERSITY OF MICHIGAN. 



Page 



Introduction I 



Description of the experiments i 



The measure of vigor 2 



Results of the experiments 4 



Other evidence relating to vigor in inbreeding 6 



Mendelian explanations of vigor 7 



Loss of vigor not accounted for by the Mendelian explanations 10 



A physiological explanation of vigor 10 



Bibliography 12 



INTRODUCTION. 



In some experiments dealing with the inheritance of certain 

 egg characters in the rotifer Hydatina senta, it has been necessary 

 to inbreed the animals a number of times in succession. Evidence 

 relating to the influence of inbreeding on vigor has thus been 

 incidentally obtained. Since this part of the evidence from the 

 experiments has no direct bearing on the inheritance of the egg 

 characters in question, it is published here separately. 



DESCRIPTION OF THE EXPERIMENTS. 



All the experiments started from a single female, herself an 

 FI from a cross. From her was bred a parthenogenetic line of 12 

 generations. Some of the females and males of this line were 

 paired, and a considerable number of fertilized eggs obtained. 

 When the fertili/ed eggs hatched, two of the earliest hatchers, one 

 from a family in which a large proportion of the eggs hatched, 



1 Contributions from the Zoological Laboratory of the University of Michigan 

 No. 139. 



