THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 193 



has been established in the case of all animals which have hitherto 

 been investigated, and of all the most carefully studied plants, and 

 finally, it has been shown to be very probable in unicellular organisms, 

 for the processes of conjugation in Infusorians and many other 

 Protozoa include phenomena verv similar to those of reducino- division 

 in the higher animals. The prediction made on theoretical grounds 

 has here been verified by observation, and it is obvious that the 

 assumption of ids, that is, of units in the germ-plasm wliicli are handed 

 on from one generation to the succeeding one, involves a reduction 

 of their number in each amphimixis. Without this the number of ids 

 would be doubled at each amphimixis, and would therefore gradually 

 amount to something enormous. We see therefore why this normally 

 recurrent reduction of ids before each amphimixis was established 

 in the course of evolution, and we see that it inevitably involves that 

 a new combination of ids should be associated with each amphimixis. 

 If nothing persists unless it be purposeful, that is, necessary, what 

 is the meaning of the fact that arrangements for amphimixis occur 

 over almost the whole known domain of life, from tlie very simple 

 organisms up to the highest, in unicellular and multicellular organisms, 

 in plants and animals alike ? Why is it that this arrangement has 

 been departed from only in a few small groups of forms, while it occurs 

 everywhere else, in almost every generation, so indissolubly associated 

 with -reproduction that it has even been regarded — with a lack 

 of clearness — as itself a form of reproduction, and is even now 

 generally called 'sexual reproduction"? And why is it that in many 

 organisms, especially lowly ones, it is not associated with e\-ery 

 reproduction, though it recurs at regular or irregular intervals? 

 Such a universal arrangement must undoubtedly be of fundamental 

 importance, and we have to ask wherein tliis importance lies. That 

 is the problem to the solution of which we must now apply 



ourselves. 



So much we may say at once : The significance of amphindxis 

 cannot be that of making nudtiplication possible, for multiplication 

 may be effected without ampliimixis in the most diverse ways— by 

 division of the organism into two or more, by budding, and even 

 by the production of unicellular germs. Even thougli these last are 

 usually in various ways so organized that they nuist undergo amphi- 

 mixis before they can develop into new organisms, yet tliere are 

 numerous germ-cells which are not subject to this condition (e.g. 

 spores), and there are -as we have seen— many germ-cells, adapted 

 for amphimixis, which always, or in certain generations, or even 

 only occasionally, emancipate themselves from this condition under 

 II. O 



