194 K. S. LASHLEY 



given by the average parental correlation of 0.101 found for 

 Hanel's clones. 



What is the significance of such a small coefficient of corre- 

 lation in an organism so subject to environmental influence as 

 is Hydra? Pearson holds that the presence of variations due 

 to environment would tend to obscure the real correlation be- 

 tween parents and offspring and hide any real inheritance which 

 might exist. My data upon the relations of variation to environ- 

 mental changes indicates that the latter may be more effective 

 in producing a likeness between close relatives than in obscuring ' 

 such a likeness.' Some conditions producing like variations in 

 parent and offspring in Hydra have been considered already. 

 Any great diversities in the conditions of the cultures would re- 

 result in a correlation between parent and progeny, even though 

 there were no inheritance of the variations studied. Such con- 

 ditions have been found by Agar in daphnids and plant lice and 

 probably account for the ancestral correlations found by Warren 

 in these forms. 



The production of a correlation in Hydra by the action of 

 diversities of environment may be illustrated by a consideration 

 of the change in the mean of clones during long periods of culti- 

 vation. Figure 5 shows that the mean number of tentacles of 

 the buds produced by Clones A and D during the first few 

 weeks of cultivation was low; that it increased gradually during 

 the first six weeks, and then decreased again. All the buds 

 produced during each of these five-day intervals were correlated 

 with one another. This gave the following results: 



Coefficient of correlation No. of pairs 



Clone A 0.0774±0.0015 95141 



Clone D 0.1313±0.0014 101872 



Correlation of all buds produced in each five day period with 

 all produced in the preceding period (a time interval correspond- 

 ing to a full generation) gives for Clone A a correlation of 0.048 ± 

 0.001 which is greater than any of the parental correlations found 

 for the initial number of tentacles. 



