EFFECT OF CONJUGATION 371 



opposed to the rejuvenating action of conjugation. JNIaupas 

 demonstrated, as we have seen, by extended experimentation, 

 that conjugation is not followed by an increase in the vigor of 

 multiplication. He found, in repeated observations, that con- 

 jugation within his degenerating stocks did not help them, but 

 attributed this to their being closely related. But he observed 

 further that when the depressed stocks that interconjugated were noi 

 related, they still died after conjugation, so that conjugation did not 

 remedy degeneration in the one case or the other ('89, p. 409). 

 He found that conjugation is often sterile (followed by death) 

 in ivild cultures of Stylonychia ('89, p. 331). He found that 

 ex-conjugants of Spirostomum, Climacostomum and Didinium 

 did not reproduce farther ('89, pp. 277, 295, 297). In Leucophrj^s 

 a large proportion of the conjugants die ('89, p. 254-255). He 

 found that in some. cases a second conjugation follows a first one 

 after but a few generations (Leucophrys, '89, p. 409). He found 

 that animals which are ready to conjugate may be prevented, and 

 the}^ will then continue to multiply with uninterrupted vigor 

 ('89, p. 306). All these observations speak against rather than 

 for the idea of a regular cycle of vegetative reproduction, result- 

 ing in degeneration, and reciuiring conjugation at a certain stage, 

 this remedying the degeneration. 



Has Maupas absolutely no evidence that conjugation reju- 

 venates? He seems possibly to have held that the following fact 

 is evidence of this effect. In his long continued cultures, he 

 found that when the animals derived from a single parent inter- 

 conjugated, they later died. It is notable that this result has 

 not been confirmed by later investigation, and Maupas himself 

 noted certain exceptions. But Maupas found that when he 

 mixed individuals from different cultures, the pairs were fertile 

 (provided both did not belong to degenerated cultures). It 

 would appear that Maupas supposed that rejuvenescence had 

 taken place in these cases. But of course there is absolutel}' no 

 evidence that such has occurred, unless it is shown experimentally 

 that the ex-conjugants are more vigorous and propagate longer 

 than similar parents who did not conjugate. In view of the 



