from work on the infusoria. It justifies the statement that the evidence is in favor of the power of these organisms to live indefinitely, if they are kept under healthful conditions. It shows that Weismann was correct in what he meant by speaking of the potential immortality of these organisms.
Thus I believe that we may feel that one of our two main questions has been definitely answered. Old age and death have no necessary place in the life of these creatures, even without conjugation.
But this brings the second question back to us with greater force than ever. What then is the effect of conjugation? What role does it play in the life of these creatures? Are we wrong in looking upon sexual union as a token of mortality?
This is the question to which I have addressed my own investigations, and with your permission I will speak next of these.
Before taking up directly the effects of conjugation, I would like to mention two subordinate points. First, in regard to the question that we have just discussed. Five years ago I started cultures from separate single individuals. During all that time there has been no opportunity for conjugation with unrelated animals, such as Maupas held to be necessary for continued life. Yet these cultures are still alive and flourishing. Thus the progeny of a single individual may certainly continue to multiply for five years without admixture from outside. This then agrees with Woodruff's results, save that Woodruff knows that there has been no conjugation of even related individuals in the line which he follows. But Maupas found, as we saw, that conjugation among the progeny of a single individual does not help, but is actually harmful; if such individuals conjugated, their doom was sealed.
But is this result of Maupas generally true? Is inbreeding among the progeny of a single individual injurious? Or did Maupas's animals die merely because they conjugated when in a dying condition?
To test this point, I caused the progeny of a single individual to conjugate together frequently. There was no evil result whatever from this. To carry the process to an extreme, I caused nine conjugations in succession within a single line, each pair being in every case the progeny of one member of the preceding pair. Thus the forefathers of the existing race have gone through the process of conjugating together nine times. Yet the progeny are as strong and well as ever.
It seems clear therefore that conjugation with close relatives is not harmful in itself, in these creatures, though repeated many times. It is of course possible that there are differences on this point among the infusoria, just as there appear to be among higher organisms. But it is certainly not a principle of general validity that inbreeding is harmful.
But now we come to the main question. What difference does conjugation make in the life of the race?