LECTURE XXIX 

 THE GENERAL SIGNIFICANCE OF AMPHIMIXIS (continued) 



Association of amphimixis witli reproduction— Origin of ampliimixis— Its lowest 

 forms— Amphimixis in Coccidia— Chromosomes in miicellular organisms -Cocc/djMw 

 prop>i"MW2— 'Amoeba-nests' as a preliminary stage to amphimixis— Plastogamy of the 

 Myxomycetes— Kesult : a strengthening of the power of adaptation— Strengthening of 

 the power of assimilation -Use of complete amphimixis— Proof of its constant efficacy 

 to be found in the rudimentary organs of Man— Allogamy— Means taken to prevent the 

 mingling of nearly related forms— Amphimixis is not a 'formative' stimulus— Attrac- 

 tion of the gei-m-cells- Effects of inbreeding compared with those of parthenogenesis— 

 Nathusius's case of injurious inbreeding— Hindrances to fertilization in the crossing of 

 sij^ecies— Probable reason for tbe injurious effect of inbreeding. 



We have endeavoured to understand why ampliimixis should 

 have been established among the processes of life, and we have now 

 to turn to the question when and how, that is, in what form, it was 

 first introduced. But first I should like to refer for a little to the 

 association of amphimixis with reproduction, which we find in all 

 multicellular organisms, and among the higher types so unexcep- 

 tionally that, until not very long ago, amphimixis and reproduction 

 were looked on as one and the same thing, and all multiplication was 

 believed to be associated with ' fertilization.' We have seen that this 

 is not the case, that on the other hand the two processes are quite 

 distinct, and may be called contrasts rather than equivalents, for 

 reproduction always means an increase in the number of individuals, 

 while amphimixis implies— originally at least— their diminution by 



a half. 



Accordingly we found that, in unicellular organisms, amphimixis 

 is not associated with reproduction, but interpolated between the 

 divisions, and not even in such a manner that amphimixis precedes 

 every multiplication by division, but so that the conjugation of two 

 animals occurs only from time to time, after numerous divisions, 

 sometimes hundreds, have occurred. It is obvious that this must 

 be so, since, if amphimixis occurred regularly Ijetween every two 

 divisions, no increase in the number of individuals would be brought 

 about, at least if the fusion of the two conjugating individuals were 

 complete. 



