Page:Popular Science Monthly Volume 80.djvu/575

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571
AGE, DEATH AND CONJUGATION

conjugation, but to the fact that he used a wild specimen, which had not been living under unadapted conditions. He apparently used the progeny of this wild individual for the remainder of his study. Now, the results I have just described show that if he had not allowed this animal to conjugate, it would have gone on multiplying just as well. Conjugation had nothing to do with the result, the fact that the specimen came from natural conditions is what counted.

Miss Cull's evidence for rejuvenescence consisted in showing that a considerable part of those that had conjugated continued thereafter to multiply. In the absence of the control experiment, she did not discover that they continue equally if they have not conjugated. There is then in this no evidence for a rejuvenating effect of conjugation.

2. To return to my own investigations, the second important result was to show that the specimens which have been allowed to conjugate multiply much less rapidly than those which have not conjugated. The difference is very marked, and showed itself in every experiment of a great number. The multiplication is slower, in those that have conjugated, for a month or two after conjugation.

This result seems surprising, in view of the widespread impression that multiplication becomes slower and slower, when the animals are kept without conjugation, and that the function of conjugation is to raise the vitality to the pitch where multiplication may continue at the normal rate. It is therefore interesting to note that those sterling investigators, Maupas and Richard Hertwig, knew well that conjugation does not increase the rapidity of multiplication. Maupas emphasizes and insists upon this fact again and again, at much length, in opposition to the prevailing view that conjugation increases the power of multiplication. What Maupas held was that conjugation saves the animals from death, though without increasing their reproductive powers. Richard Hertwig observed, correctly, that conjugation actually decreases the rate of multiplication.

3. A third result of comparing those that have conjugated with those that have not is that many more of the former die or are abnormal than of the latter. In a specially favorable experiment, out of 61 conjugants, eleven lines had died out completely in 33 days, while of 59 lines that had not conjugated, but were otherwise similar, none had died in the same period.

4. Usually a considerable number of the conjugants never divide after conjugation, while all of those that have not conjugated continue dividing.

5. There is much greater variation among the progeny of those that have conjugated than among those that have not. This greater variation shows itself (1) in the rate of multiplication; (3) in dimensions. If we determine the coefficients of variation, we find these much greater in the progeny of those that have been allowed to conjugate.