222 THE EVOLUTION THEORY 



case there must be growth subsequent to the conjugation before the 

 normal is re-attained. It ma}^ be doubted, therefore, whether the 

 increase in mass is, even in tlie case cited, the essential event in 

 conjugation, and whetlier there are not other effects whicli we cannot 

 clearly recognize. Here, too, there must be differences between the 

 two conjugating individuals, as we have just seen, for if they only 

 communicated something similar to each other, the result would he an 

 increase only in their mass, not in their qualities. 



Althoufi'h we cannot demonstrate differences of this kind in the 

 case of the lowly organisms Avith which we are now dealing, we may 

 assume their existence from analogy with the higher organisms. 

 We know, especially through G. Jager, that in Man every individual 

 has a specific exhalation, his particular odour, and that in the secretions 

 of his glands there are incalculably minute differences in chemical 

 composition, which justify the conclusion that the living substance 

 of the secretino- cells themselves exhibits such differences, and that 

 all the various kinds of cells in an individual are not absolutely 

 identical with the corresponding cells of another individual, but that 

 they are distinguished from tliem by minute yet constant chemical 

 differences. The assumption that difterences of this kind exist even 

 in unicellulars, and in all lowly organisms generally, is not a merely 

 fanciful one, but has much prol)al)ility. 



How far the combination of these individual differences of 

 chemical, and at the same time vital, organization is able to quicken, 

 to strengthen the metabolism, to bring about ' physiological regene- 

 ration,' or whatever we may choose to call it, we do not yet understand. 

 It has been said that in plastogamy an exchange of ' substances ' takes 

 place ; that each gives to the other the substances whicli it possesses 

 and the other lacks, and that this causes an increase of vital energy. 

 But it is unlikely that we have here to do merely with chemical 

 substances, although these, of course, as the material basis of all vital 

 processes, are indispensable ; it seems to me more prol^able that the 

 vital units (biophors) themselves in their specific individuality must 

 play the chief part. But even this is saying very little, for we have 

 not yet reached an understanding of these processes, and if we were 

 not forced by the fact of plastogamy to the conclusion that this union 

 must have some use, no one would liave been likely to postulate 

 it as useful, still less as necessary. It has, of course, been frequently 

 suggested that multiplication by ffssion, if long-continued, results 

 in 'exhaustion,' and that this is corrected by amphimixis, but who 

 can tell why this ' exhaustion ' might not be remedied, and even more 

 effectually remedied, l)y a fresh supply of fuel, that is, of food ? One 



