334 THE EVOLUTION THEORY 



that is concerned, yet in almost all animals and plants it consists of 

 such a minimal quantity of living matter that it is unable to build up 

 a new multicellular organism by itself. Only in one alga [Ectocarpus 

 siliculosus) has it been observed that not only the female germ-cell 

 can develop parthenogenetically under certain circumstances, but that 

 the male-cell may also do so. In this case, however, the difference 

 in size between the two is not great, and it is noteworthy that the 

 male plant, in correspondence with the smaller size of the zoosperm, 

 tends to be a somewhat poorly developed organism. 



If we are forced to the conclusion in regard to multicellular' 

 organisms that amphimixis does not supply the power of develop- 

 ment to the ovum, but that, on the contrary, the power of develop- 

 ment is withdrawn from the ovum, so that amphimixis can, so to 

 speak, be forced, must we not assume something similar for unicellular 

 organisms also ? May not amphimixis be made compulsory in their 

 case also, in that the Infusorians in preparation for conjugation go 

 through changes which make their unlimited persistence possible 

 only on condition that they conjugate? In my opinion the division 

 of labour in the nucleus, which is differentiated into a macronucleus 

 and a micronucleus, and the transitory nature of the former, may 

 be regarded as an adaptation in this direction. In any case, it is 

 striking that an organ which otherwise persists without limit among 

 unicellular organisms, the nucleus, is here subject to natural death 

 after the manner of the body of multicellular organisms, that it 

 breaks up and must be reformed from the micronucleus which in 

 this case is alone endowed with potential immortality. I am inclined 

 to regard this as an arrangement for compelling conjugation, since 

 it is only after conjugation that the micronucleus forms a new macro- 

 nucleus, although the latter is indispensable to life, as we see from 

 experiments in dividing Infusorians artificially. 



Suppose we had to create the world of life, and it was said to us 

 that amphimixis must — wherever possible — be secured periodically to 

 all unicellular and multicellular organisms, what better could we do 

 than arrange devices which should exclude individuals which, by 

 chance or constitution, could not attain to amphimixis from the 

 possibility of further life ? But would amphimixis then be the cause 

 of persistence or a principle of rejuvenescence 1 



I do not see that there can be any ground for such an assumption 

 other than the tenacious and probably usually unconscious adherence 

 to the inherited and deep-rooted idea of the dynamic significance of 

 ' fertilization,' no longer, perhaps in its original form, which regarded 

 the sperm as the vital spark which awakened new life in the dead 



