INHERITANCE IN ASEXUAL REPRODUCTION 203 



leaves no doubt that the existence of diverse races within the 

 species is a general condition in all phyla. 



The problem of inheritance of variations within the clone 

 presents much greater difficulties and there is much conflict 

 between the results of different investigators. The work of 

 Whitney has shown that in Hydatina diverse strains may arise 

 in a clone descended from a single fertilized egg and Calkins and 

 Gregory report similar results for Paramecium. In these cases 

 there is, however, no intimation that the inheritance of variations 

 is a general characteristic of asexual reproduction or that the 

 change is the result of the accumulation of slight variations. 

 The four studies in which there is an appearance of inheritance 

 of continuous variations within the pure line or clone are those 

 summarized by Pearson in 1910; the studies of Johannsen on 

 beans, Warren on Daphnia and Hyalopterus, and Hanel on 

 Hydra. In all this work the evidence for inheritance can be 

 drawn only from the ancestral correlations, while the evidence 

 from the effects of selection seems to point the other way. The 

 question of the relative values of the coefficient of correlation 

 and of selection experiments hence becomes of great importance. 



In Agar's recent study of inheritance in parthenogenesis, 

 where great precautions were taken to rule out the influence of 

 environmental agents, there is no significant correlation between 

 parent and progeny within clones of Cladocera and sufficient 

 evidence of environmental causes of correlation is presented to 

 account for Warren's results with Daphnia. For Aphids he 

 finds, with Warren, a slight ancestral correlation but the evi- 

 dence for an environmental cause of this correlation, while per- 

 haps not absolutely conclusive, is sufficient to make the ancestral 

 correlation in these forms of very doubtful value as an index of 

 inheritance. Swing's selection experiments with Aphis avenae 

 offer further evidence against the inheritance of variations in 

 these forms. 



The results recorded in the present paper are quite in accord 

 with those of Agar on Cladocera and show that for Hydra 

 also the ancestral correlation is untrustworthy as a measure of 

 inheritance. 



