he followed thus its history from generation to generation. The creatures divided every eighteen hours or so, and for about a hundred generations they remained strong and healthy. Then sickly and deformed individuals began to appear here and there; these became more and more numerous, till finally all had degenerated thus; they died out completely at the end of five months, after 215 generations. Another series, beginning with an animal that had just conjugated, degenerated and died at the end of 316 generations; and other series gave similar results.
Thus, said Maupas, it is clear that these creatures do get old and die, just as higher animals do. The idea that they are potentially immortal is a mistake; death inheres in the process of life.
But why then are not these creatures all dead? How is it that they exist at the present time?
The key to this is found, according to Maupas, and according to the suggestions of many before him, in the process of sexual union. As fertilization saves the life of the egg and permits it to continue dividing for many generations, so does conjugation put new life into the dying infusorian, permitting it also to continue multiplication for many generations. The existence of sexual union in these creatures finds its explanation in the fact that they, like ourselves, are mortal; and their mortality is overcome, like our own, by the process of sexual reproduction. Their lives begin with the strength of youth, and inevitably run down the incline of age, as do our own.
But Maupas was one of those men who are not satisfied with a brilliant hypothesis; if conjugation actually restores vitality, he wanted to see it done. He allowed one of his Stylonichias in the 156th generation to conjugate with another that he captured wild. Then he took one from this pair and allowed it to multiply. Most unfortunately he does not say (doubtless he did not know) whether it was the old one or the fresh one that he allowed to continue. But this creature, which had just conjugated, propagated itself for 316 generations before it finally died of old age. Meanwhile, the rest of the old stock, which had not been allowed to conjugate with fresh individuals, died out in 59 generations.
Thus it appeared to be demonstrated that conjugation restores vitality, that it rejuvenates. The brilliant hypothesis had seemingly become the demonstrated reality.
But it is interesting to the student of the history of science, and of scientific certainty, to discover that many years before the time of Maupas the function and effect of conjugation had been completely worked out in detail, by the most painstaking investigations, so that in 1862 a statement for it could be made that, according to the competent judgment of Engelmann, had been by a great abundance of observa-
