THE GENETICS OF A DAPHNIA HYBRID DURING 

 PARTHENOGENESIS. 



By W. E. agar. 



Professor of Zoology in the University of Melbourne. 



(With Three text-figures.) 

 CONTENTS. 



PAGE 



Introduction , 303 



Some points in the Biology of the Cladocera which concern the 



present experiments ......... 304 



Cultural methods 306 



The experimental data ......... 306 



Material and characters employed 306 



The production of the hybrids 312 



Genetics of the hybrid clone Xc ...... 314 



Inheritance within the hybrid clone Xc .... 318 



The genetics of another hybrid clone ..... 327 



Discussion ............ 327 



Summary 330 



Beferences to Literature 33Q 



Introduction. 



On the hypothesis, now supported by such a mass of indirect evidence, 

 that segregation of hereditary factors is due to the segregation of homo- 

 logous chromosomes in meiosis, it is clear that there should be no such 

 segregation in parthenogenetic reproduction unaccompanied by reduction 

 of the chromosomes. The determination of whether or not segregation 

 does occur under these circumstances may indeed be considered a crucial 

 test of the truth of the hypothesis. At present there exists very little 

 direct evidence on this point, at any rate for the animal kingdom. 



For many years I have been conducting experiments with Cladocera, 

 in which both males and females are produced parthenogenetically 

 without reduction of chromosomes, with the purpose of solving this 

 problem for this group of animals. It is however only recently that 

 I have succeeded in obtaining the hybrids necessary for its direct 

 solution, though indirect evidence of the absence of segregation in 

 parthenogenesis in this group was presented in my paper of 1914. 



