186 K. S. LASHLEY 



of ages at death shown in figure 6. The irregular form of the curves 

 and the fact that the vast majority of the polyps died at a relatively 

 early age scarcely speaks in favor of an 'Altersschwache.' The curves 

 are similar enough in form to suggest that the deaths were due to two 

 periods of unfavorable conditions (a and h) in his cultures. 



At no time have I observed an epidemic of depression in the 

 individual cultures belonging to the same clone; less than 1 per 

 cent of the polyps have shov^n depression and always the closest 

 relatives of these remained normal, a condition which is not at 

 all in harmony with theories of- clonal senescense. Further, 

 during the four months that the clones were kept under obser- 

 vation, including more than 20 asexual generations, there was no 

 significant change in the character of either clone. The repro- 

 ductive rate, the first character modified by a reduction of the 

 vitality of the polyps, was as high at the end of the experiment as 

 at the beginning. This furnishes some evidence against the 

 belief that the diversities are due to the clonal age but it is not 

 conclusive.^ 



The existence of other races 



A comparison of the standard deviations of the Clones A and 

 D reveals the fact that clone A was always the more variable 

 of the two. This difference suggested that Clone A was not pure 

 and an examination of other evidence quickly confirmed this 

 view. The variations of the clone tended to a dimodality which 

 does not appear in any other race studied and the greater varia- 

 bility and dimodal form of the variation curve did not persist 

 in Clone A' which was descended from a single polyp taken 

 from Clone A. The records of the clone were reviewed in order 

 to test whether the greater variability was characteristic of the 

 race or was the result of the inclusion of diverse types as is sug- 

 gested by the condition in Clone A\ One subordinate clone 

 represented by the direct line of descent AlA2blala2ala (the 



^ Agar ('14) has shown that diverse clones produced by parthenogenetic re- 

 production may be produced by different eggs hatched at the same time. The 

 differences here are clearly not due to the ages of the clones. Lang ('92) found 

 that only one germinal layer of Hydra takes part in the formation of the buds, 

 and this work, while unconfirmed, suggests that the differences between partheno- 

 genesis and budding may not be so great as is generally supposed. 



