INHERITANCE IN ASEXUAL REPRODUCTION 



161 



The experiment upon regeneration likewise fails to support 

 the conclusion which Hase draws from it, since it shows only that 

 the number of tentacles is not regenerated at its full value but 

 fails to disprove that the number regenerated is not proportional 

 to the original number. I have reviewed the experiments of 

 Hase in some detail because they have been generally quoted as 

 proving that the number of tentacles of Hydra is not an heredi- 

 tary character, whereas, at best, they but serve to cast some doubt 

 upon Hanel's conclusions. 



TABLE 1 



Increase in the average number of tentacles of buds produced 

 while their parents bore the numbers increasing from 

 5 to 9 {modified from Hase) 



NUMBER OF TENTACLES BORNE BY 

 PARENTS 



MEAN NUMBER OF TENTACLES OF 



BUDS PRODUCED WHILE THE PARENTS 



BORE THE NUMBER OPPOSITE 



5.60 

 5.63 

 6.33 

 5.80 

 6.32 



A much more serious criticism of Hand's work, and of 'pure 

 line' work in general, was made by Pearson during the follow- 

 ing year. He subjected Hand's data to a more thorough analj^sis 

 than she herself had done and held that they by no means justi- 

 fied the conclusions drawn. Concerning the evidence for the 

 existence of strains, diverse with respect to tentacle number, he 

 says: 



Hanel begins with a very careful investigation of the growth and 

 environmental changes in the character selected, the number of tentacles 

 of Hydra grisea. There is a general agreement with Parke's results 

 that the number of tentacles changes with age, size, food and place of 

 culture. Differences in these factors can produce very considerable 

 differences in individuals and differences in the averages of differentially 

 treated groups which can amount to as much as 0.5 to 0.8 of a tentacle. 

 These are preciselv the order of the average hereditarj^ differences. 

 Thus: 



