XII.] CONJUGATION AND SEXUAL REPRODUCTION. 213 



Since this process is in direct antagonism to reproduction, i.e. 

 increase, it can onl3^ be repeated after long intervals, lest it 

 should prevent the sufficient increase of a colony of such animals. 

 Hence we find that conjugation recurs periodically among the 

 Protozoa ; and indeed— as Maupas has taught us in the Infuso- 

 ria—only repeats itself after a great many (120-300) generations. 



Amphimixis, as we have seen, only became possible among 

 Metazoa by concentrating or packing all the predispositions into 

 the restricted area supplied by the nuclear substance of a single 

 cell,— and this must happen even when the adult body is com- 

 posed of millions of cells, differentiated in the most diverse 

 directions, and combined to form tissues, organs, and systems. 

 The result of this arrangement is seen in a highly complex 

 ontogeny ; and it is obvious that many conditions of life may 

 arise which render it advantageous that the increase of the 

 species should not proceed exclusively by this long and intricate, 

 and therefore dangerous road, and that accordingl}' the origin 

 of each new individual should not be necessaril}'' bound up with 

 amphimixis. In this way we are able to understand the wide 

 distribution and diverse forms of asexual reproduction among 

 the lower Metazoa and in plants. 



There is, however, another factor, — the appearance, in the two 

 last-mentioned groups, of that complex form of individuality 

 known as the stock. This is brought about by the budding or 

 division of the person, a form of increase which renders possible 

 a continuity of the persons proceeding from one another. Such 

 increase is not associated with amphimixis, because the indis- 



' superficielle,' etc. I have never held such a view ; the onh' passage in 

 my writings which can have given rise to such a misapprehension deals 

 with the ph3detic origin of conjugation (' Bedeutung der sexuellen Fort- 

 pflanzung, p. 52, translated in vol. i, see pp. 293-294). Anyone who 

 refers to this passage will find a h^'pothesis, expressed with all reserve, 

 suggesting the original significance of the fusion of two unicellular 

 organisms. Conjugation must have had some beginning, and although 

 I believe that in its present form it signifies a source of variability, it 

 must originally have had some other meaning, for two Monera would 

 scarcely coalesce in order to ensure variability' in their descendants. 

 A change of function must have taken place, or, as Dohrn has very 

 clearly expressed it, a secondary effect associated with the original main 

 eff'ect has, at a later date, usurped the place of the latter. Maupas 

 accepts conjugation in the form in which it exists, and makes no attempt 

 to understand how it originated. I do not blame him for this, but is it 

 really so superficial to investigate the origin of an}' phenomenon ? 



