W. E. Agar 327 



The Genetics of another hybrid clone. 



In addition to the hybrid clone Xc just described, another {Xf) was 

 obtained from the reciprocal cross D. pulex x D. obtusa. This clone had 

 all the general characteristics of the clone Xc, but the partial sterility 

 of the females was even more marked, so that indeed I failed to maintain 

 the clone for more than four generations, and during that time obtained 

 very few specimens. 



The mean -j ratio for the eleven females measured was 2*24. Only 



four males were obtained, and of these only three (all sterile) survived 



for measurement. Their mean ^ ratio was 11"23. 



Discussion. 



The experiments just described form a confirmation of my former 

 experiments on inheritance in parthenogenesis (1914). The most com- 

 plete of these employed another Cladoceran, closely related to Daphnia, 

 namely Simocephalus exspinosus. A large number of ephippia, each of 

 which in Simocephalus contains a single fertilized egg, were collected and 

 hatched, and a population was constructed of 57 clones, each descended 

 from one of these fertilized eggs. This was termed the polyclonal popu- 

 lation, and was bred for five generations. The parental correlation co- 

 efficients for the factors size at birth and at maturity, were found for each 

 of the four pairs of generations (1 and 2, 2 and 3, 3 and 4, 4 and 5). The 

 three possible grandparental correlations, two great-grandparental and 

 one great-great-grandparental correlations were also found. All the 

 correlation coefficients, for all degrees of ancestry, were sensibly equal 

 (Table VIII). 



TABLE VIII. 



Mecm correlation coefficients for the polyclonal population ofS. exspinosus. 



Size at Birth Size at Maturity 



Parental -410 -395 



Grandparental -892 -413 



Great-grandparental ... ... 408 '505 



Great-great-grandparental ... -430 — 



The conclusions to be drawn from these figures are that the original 

 57 females which gave rise to the 57 clones belonged to a number of 

 different genotypes which reproduced their characters generation after 

 generation, so far as they were not obscured by environmental modifica- 

 tions (if these had been absent the correlation coefficient must have been 



