36 THE AMERICAN JOURNAL OF SOCIOLOGY
reported by Maupas 1 that certain infusorians are capable of reproducing asexually for a number of generations, but that unless the individuals are sexually fertilized by crossing with unrelated forms of the same species they finally exhibit all the signs of senile degeneration, ending in death. 2 After sexual conjugation there was an access of vitality, and the asexual reproduction proceeded as before. "The evident result of these long and fatiguing experiments is that among the ciliates the life of the species is decomposed into evolutional cycles, each one having for its point of departure an individual regenerated and rejuvenated by sexual copulation." 3 The results obtained by Maupas receive striking confirmation in the universal experi- ence of stock breeders that in order to keep a breed in health it is necessary to cross it occasionally with a distinct but allied variety. It appears, then, that a mixture of blood has a favor- able effect on the metabolism of the organism, comparable to that of abundant nutrition, and that innutrition and in-and-in breeding are alike prejudicial. If this is true, and if heightened nutrition yields an increased proportion of females, we ought to find that breeding out is favorable to the production of females, and breeding in to the production of males ; and a considerable body of evidence in favor of this assumption exists. 4
1 E. MAUPAS, "Thdorie de la sexualitd des Infusoires elites," Comtes Rendus, 1887, Vol. CV, pp. 356 seq.
'The extinction took place at about the 330th generation in onychodromus gran- dis, at about the 320th generation in stylonichia mytilis, at about the 330th generation in leucophrys patula, and at about the 66oth generation in oxylricha (indeterminate). MAUPAS, loc. '/., p. 358.
3 MAUPAS, loc. cit., p. 358.
The celebrated experiments of Maupas, taken in connection with recent investi- gations of Klebs, illustrate the fact that the phenomena characteristic of any given form can rarely be generalized. Klebs' experiments on a/gce have shown that the same form can be rendered sexual or asexual at will. No sexual organs are produced in feeble light or in running water. The same form which reproduces sexually in stag- nant water reproduces asexually and indefinitely in running water. (KLEBS, loc. cit., p. 1 6.) It does not appear, however, that Maupas' conclusions are affected by this fact.
4 WESTERMARCK, loc. cit., pp. 476-83, following a suggestion of Busing, has brought together much of the evidence on this point, but the application of the facts here made has not, I believe, been suggested.
