THE IMPORT OF CONJUGATION. 103 



and watched for five months. The usual number of suc- 

 cessive generations occurred. On to the one hundred and 

 thirtieth generation, members were removed at different 

 stages, and were observed to conjugate successfully with 

 unrelated forms. But when the family began to draw near its 

 end, even removal to fresh conditions was without effect. 

 About the one hundred and eightieth generation, the 

 strange sight was seen of individuals of the same family 

 attempting to unite with one another. The results were, 

 however, nil, and the conjugates did not even recover from 

 the effects of their forlorn hope. 



Without the normal sexual union, then, the family becomes 

 senile. Powers of nutrition, division, and conjugation with 

 unrelated forms, come to a standstill. This senile degenera- 

 tion is very interesting. The first symptom is decrease in 

 size, which may go on till the individuals only measure a 

 quarter of their normal proportions. Various internal struct- 

 ures then degenerate, " until at last we see formless abor- 

 tions, incapable of living and reproducing themselves." The 

 nuclear changes are no less momentous. The more important 

 micro-nucleus may partially or completely atrophy, and con- 

 jugation is therefore sterile. The larger nucleus may also 

 become affected ; " the chromatin gradually disappearing." 

 Physiologically, too, the organisms become manifestly 

 weaker, though there is what M. Maupas calls a " surex- 

 citation sexuelle." Such senile decay of the individuals and 

 of the isolated family inevitably ends in death. 



The general conclusion is evident. Sexual union in those 

 infusorians, dangerous perhaps for the individual life, and a 

 loss of time so far as immediate multiplication is concerned, 

 is absolutely necessary for the species. The life runs 

 in cycles of asexual division, which are strictly limited. 

 Conjugation with unrelated forms must occur, else the 

 whole life ebbs. Without it, the Protozoa, which some 

 have called "immortal," die a natural death. Conjuga- 

 tion is the necessary condition of their eternal youth 



