172 On the Genetics of the Ciliate Protozoa 



tend to be different. But biometric proof is now offered that the progeny 

 of one member of a pair of conjugants tend to be like the progeny of 

 the other, owing to the hereditary influence of both " parents " (con- 

 jugants) on all the progeny. It thus appears that conjugation simul- 

 taneously produces uniformity and diversity. I take this paradox to 

 mean that if two similar individuals of the same race conjugate, then 

 the ])rogeny of both will ditt'iT fniiii the original race, though the 

 progeny of one will resemble the progeny of the other in whatever 

 respects it diff'ers from the original race. Or, in other terms, a pair 

 of conjugants a, and a„, belonging to a race a, produce after conjugation 

 progeny forming races bi and h., — differing from a, but resembling one 

 another in both being b. 



lOS. Both the fundamental conclusions reached by Jennings appear 

 to me unproved. My chief difficulty is that I cannot find convincing 

 evidence of a single concrete instance in which, from a known race — 

 constant in a certain character — a new race — permanently diverse in 

 this character — has arisen as a result of conjugation. As an abstract 

 biometric proposition, it is no doubt demonstrated "that conjugation 

 among the members of a pure race does result in differentiations that 

 are inherited," so that from a uniform race diverse races might seem to 

 arise. Now the diversity of the new races is manifested mainly in 

 (1) mortality, (2) size, (3) rate of fission. In the first case, Jennings 

 (like others) has found that many exconjugants, or their immediate 

 descendants, die. The consequence of conjugation in these cases is 

 really death. It is true there is increased variation in mortality among 

 the progeny, but the individuals which manifest this diversity merely 

 die out, so that no new races are produced in this fashion. Concerning 

 the second character — size — the evidence' seems to me unsatisfactory. 

 All that it appears to show is that although conjugants are smaller 

 than non-conjugants of the same race, their progeny are not : and that 

 there is greater variability in the size of individuals formed by fission 

 from exconjugants during the first few days after conjugation, than is 

 seen in the progeny of ordinary non-conjugants. Definite evidence of 

 the production of a new race of permanently different size — as a result 

 of conjugation — I can nowhere find. Perhaps the best is that which 

 can be extracted from the paper of Jemiings and Lashley (191:3 a), from 

 which it can be inferred that the descendants of 43 pairs of exconjugants, 



' .Jennings (1911a). Further evidence is given in 1913 (expt. 9), but of this .Jennings 

 himself says "the results there given are by no means conclusive, the matter requires 

 further study." 



