SEX IN INFUSORIA 231 



the preconjugants — is applicable, I believe, to all the rest of the 

 Infusoria. We have already seen the very marked differences 

 which characterize the preconjugants of 0. janus in com- 

 parison with the neuter specimens. The same differences, 

 though less evident, exist in other Ophryoscolecidae (in all the 

 three species studied by me) : and some further indications 

 of the existence of preconjugants in other forms are scattered 

 here and there in different papers on Infusoria ; but I do not 

 intend to discuss them in this prehminary note. 



The conception of sexual puberty preceding conjugation 

 casts a new light on the question of experimental induction 

 of conjugation by means of different external stimuli (hunger, 

 &c.). In all such cases the specimens treated in the experiment 

 evidently remain still unable to conjugate, whatever be done 

 to them ; but the stimuli apphed to the Infusoria make them 

 begin the progamic fission, which produces sexually mature 

 individuals ready for conjugation. It is noteworthy that the 

 cases of ' reconjugation ' prove this sexual maturity to persist, 

 in some exceptional cases, even after conjugation has occurred. 



There is a further point to be discussed, although I do it 

 with some reserve. I refer to the heightened viability of the 

 conjugants as compared with the rest of the population. The 

 high mortality amongst exconjugants is already known. In 

 my material also dying exconjugants are often to be found ; 

 in Ophryoscolecidae they are easily recognized by many striking 

 characters, as I shall show in another note. The same symptoms 

 of death are observed in many (17 per cent.) of the neuters. 

 The conjugating pairs, on the contrary, were never found in 

 a dying condition. This circumstance makes me believe 

 that the stages of sexual puberty and conjugation are the most 

 viable. If this is so, we can easily understand why ciliates 

 acquire a tendency to conjugate in bad conditions of life ; for 

 the processes of progamic fission and conjugation would enable 

 the animals to acquire, for a couple of days, a heightened 

 resistance to harmful external conditions. It remains to test 

 this experimentally on some free-living Iniusoria. If we accept 

 this hypothesis the cases of reconjugation are easily explained : 



NO. 266 R 



