C. DOBBLL 173 



measured 25 days after conjugation, all possessed a smaller mean size 

 than that of the race from which they were derived. The number of 

 individuals measured is not great, however, and one may doubt whether 

 permanently smaller races^ had been produced as a result of conjugation. 



109. Concerning the third character — rate of fission — the evidence 

 appears at first sight conclusive. The biometric results show clearly 

 that there is a difference (greater variability) in the fission rate of the 

 descendants of exconjugants as compared with those of non-conjugants 

 or split conj ugants — all of the same pure line. But as Jennings himself 

 points out " conjugation increases the variation mainly toward the lower 

 extremity of the range" — that is, the effect of conjugation is to retard 

 the rate of fission. Is not this merely another aspect of the same 

 condition which is otherwise manifested as " high mortality " and " loss 

 of vigour" after conjugation? Jennings's "Experiment 6" seems to 

 me the key to the matter. " This exjDeriment as a whole shows the 

 fact that after conjugation the organisms are in a condition such that 

 many may die, while those that have not conjugated live ; and the 

 further fact that the rate of reproduction is made slower by conjugation, 

 remaining in this condition for about two months," after which it " has 

 regained about the usual rate." If the result of this experiment may 

 be regarded as typical, then it indicates that the lowering in fission rate 

 following conjugation is transient, recovery occurring sooner or later. 

 It is demonstrated that after conjugation the organism and its progeny 

 are weaker, or less resistant to external conditions (shown by higher 

 mortality, lagging fission rate, unstable size, abnormalities, etc.) for a 

 certain time ; and that complete recovery to the normal state preceding 

 conjugation occurs subsequently : but I find no proof that from a race 

 with a given fission rate, another race with a permanently different 

 fission rate has arisen as a result of conjugation'-. 



110. Turning now to Jennings's second proposition (§ 107), I can 

 make criticisms of only a very general nature. I am not able to judge 

 of the validity of the biometric methods employed for its demonstration. 

 It appears to me, however, that to prove " biparental inheritance," the 



' The fact that all the races are smaller is significant. One can hardly suppose that 

 conjugation in this race always leads to a permanent reduction of size. It seems much 

 more likely that there was some environmental factor (e.g. food or temperature — cf. §§ 60, 

 66 et seq.) affecting all the cultures alike. 



2 A similar criticism to the above has already been made by JoUos (1913 a). It seems 

 to me unfortunate that Jennings should have selected for his chief study a physiological 

 character— fission rate — which is so greatly influenced by environmental conditions (§ .51 

 et seq.). 



Journ. of Gen. iv 12 



