AGE, DEATH AND CONJUGATION S75 



(2) But, secondly, fertilization brings about in some way inheritance 

 from two parents. "When there is inheritance from but one parent, the 

 inheritance is as it were complete; the child as a rule resembles its 

 parent in all liereditary characteristics ; this is the result of the so-called 

 " pure line " work. But when we have biparental inheritance, a great 

 number of different combinations of the characteristics of the two 

 parents are produced, so that the process of fertilization is one that in 

 this respect completely alters the face of organic nature, producing 

 infinite variety in place of relative uniformity. 



These two functions of fertilization, the initiation of development, 

 on the one hand, the production of inlieritance from two parents, on 

 the other, are logically independent; they might conceivably be per- 

 formed at different times and by different mechanisms. The fact that 

 in many organisms the same mechanism that brings about biparental 

 inheritance is likewise the one that initiates development might from 

 certain j^oints of view be called an adaptation. Its result is to insure 

 that in all the organisms that develop there shall be inheritance from 

 two parents, not from one. In the work on artificial parthenogenesis 

 these two functions have been separated experimentally; the initiation 

 of development takes place alone. 



Now, in endeavoring to understand conjugation, attention has been 

 given hitherto almost exclusively to the first of these two functions. 

 It was held that the function of conjugation must be to make possible 

 life and development where it was otherwise impossible, just as fertiliza- 

 tion arouses the egg to further life and development. But it turns out 

 that conjugation, instead of having this one of the two functions of 

 fertilization, has the other. The two functions are in the infusorian 

 separated, just as they are in artificial parthenogenesis, but it is the 

 second, not the first, that we have before us. Conjugation is not 

 necessary in order that life and reproduction shall continue; they 

 continue without it. 



But the life which thus continues is uniform and unchanging. 

 To give biparental inheritance, with varying mixtures of the character- 

 istics of the two parents; to produce these new combinations in great 

 variety, conjugation is necessary. And when this happens under such 

 conditions that the original combinations were not adapted to survival, 

 then some of the new combinations produced often are adapted to the 

 conditions; conjugation then results in a survival of an organism that 

 would have been completely destroyed without it. It is most interest- 

 ing in this connection to observe that conjugation is usually induced 

 by an unfavorable change of conditions, a change of such a nature that 

 the organisms begin to decline. Thereupon conjugation occurs, so 

 that new combinations are produced, adapted to varied conditions, 

 some of which may survive. 



Thus it appears to me that the whole series of investigations on old 



