224 THE EVOLUTION THEOKY 



gamy, i. e. in the mere coalescence of the protoplasmic bodies. But, 

 as it seems to me, we have not yet clearly recognized what the 

 advantage precisely is; we do not yet see how such a mingling 

 or combination of two plasms should every time be of advantage 

 for the combined conjugate. If we assume with Zehnder that two 

 kinds of ' nutritive' biophors are brought together which differ slightly 

 from each other in digestive capacity, three cases may occur. Either 

 the food a, adequate for the animal A, is just as abundant as the 

 food b, suitable for the animal B, and then half the conjugated animal 

 will be nourished by means of the biophors a, the other half by means 

 of the biophors b, and the state of matters is the same as it was 

 before conjugation ; or the food b is more abundant than the food a, 

 or conversely, and then the biophors b will have to take the larger 

 share in the nourishment of the conjugate A + B, and they will 

 therefore multiply more rapidly and the biophors a will decrease 

 relatively in number. Nutrition and growth will then go on more 

 slowly for a time, but will soon attain to their former intensity. The 

 combined individual A+B has then certainly gained an advantage 

 over the isolated animal A, and the living substance of A which, 

 if left to itself would probably have perished, can continue to live 

 in combination with B. But in that case it is not obvious where 

 the advantage in the union can lie, as far as B is concerned. An 

 advantage to B only results if there be a combination not of one kind 

 of biophor only, but of several or many kinds of biophors. If for 

 instance A, whose digestive biophors were weak, brought with it into 

 the partnership ' secretory ' or nervous biophors stronger than those of 

 B, then there would be an advantage for both in the combination, 

 and it is thus that, in the meantime, I interpret the direct benefit 

 which results from pure plastogamy. This benefit must be the more 

 important and far-reaching the longer multiplication by fission con- 

 tinues without the occurrence of conjugation. 



We thus reach what is perhaps a not wholly unsatisfactory con- 

 ception of amphimixis, in so far at least that we do not require 

 to assume that there has been a fundamental change in its significance 

 between its expression in the lowest organisms and in the higher and 

 even highest forms. Everywhere it is the same advantage: an increase 

 in the power of adaptation ; but it sometimes finds expression directly 

 in the product of conjugation, sometimes only indirectly, sooner or 

 later, among the descendants of the product. 



How far below the Myxomycetes pure plastogamy reaches we do 

 not know ; whether it also occurs among non -nucleated organisms 

 (Haeekel's Monera) we cannot tell from experience, since these 



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