220 THE EVOLUTION THEORY 



cell-sub.stance, after having Iteeii siirrouiided for a very long time 

 with the same cytoplasm. If this were the import of amphimixis, 

 then an exchange of nuclei would take place, and this we find nowhere 

 even among the lowest forms of life, for everywhere there is a union 

 of the nuclear substance of two individuals. But this is by the way 1 

 Further cases of plastogamy have been observed in many of the limy- 

 shelled Rhizopods. A union of this kind does not usually lead to any 

 visible consequences, but in some Foraminifera a group of young 

 animals is developed within the cell-l)odies by the division of the 

 nuclei and the cell-body ; thus multiplication follows the fusion just 

 as in pei-fect amphimixis, and we may therefore assume that there 

 is a causal connexion between tlie two. In the slime-fungi, too, 

 the union of several amceba-like cells into a multi-nucleated Plas- 

 modium is followed later by the development of numerous encapsuled 

 spores, but only after the plasmodium, which to begin with is micro- 

 scopically small, has grown to a macroscopically visible, reticulated 

 mass (.£thaliuin) sometimes a foot in extent. In this case the fungus, 

 creeping slowly over its foundation of decaj^ing substance, takes up 

 nourishment from it, and it is not possible to tell whether the union 

 of the amcKba? 3'ields any further advantage than that of facilitating 

 the spreading over large uneven surfaces, and through this, later, 

 the development of large fruit-bodies. But in the case of the Forami- 

 nifera the plastogamy has obviously another effect, unknown and 

 mysterious, which as yet no one has ever been able to define precisely. 

 Words like ' stimulus to growth,' 'stimulating of the metabolism,' and 

 even ' rejuvenation,' give no insight into what happens, but that 

 something happens, that through the fusion of two or more uni- 

 cellulars a stimulus is exerted, which reveals itself later in increased 

 rapidity of growth, we may, and indeed nmst assume, because this 

 process has become a permanent arrangement in so many unicellular 

 organisms. Only what is useful survives, and the uniting individuals 

 must derive some advantage from the process of fusion, and it remains 

 to be seen whether we can find out with nuy clearness what this 

 advantaoe niav be. 



Till within a few decades cigo it was believed that in this process 

 one individual devoured the other, but this can now no longer be main- 

 tained. If any one still seriously considers this possible, Schaudinn's 

 observations would convince him of his error, for in Trichot>p]icerlurn, 

 a marine, many-nucleated Rhizopod, he observed, on the one hand, 

 the union of two or more animals, i. e. plastogamy, and on the other 

 hand, the swallowing and digesting of a smaller member of the species 

 by a larger one — two processes which are absolutely difterent, for in 



