286 THE SIGNIFICANCE OF SEXUAL REPRODUCTION 



w ell to remember that parthenogenesis is now the only method of 

 yeproduction in many species (although we do not know the period 

 of time over which these conditions have extended), and is neverthe- 

 less unattended by any perceptible decrease in fertility. 



From all these considerations we may draw the conclusion that 

 the process of rejuvenescence, as described above, cannot be accepted 

 either as the existing or the original meaning of conjugation, and 

 the question naturally arises as to what other significance this 

 latter process can have possessed at its first beginning. 



Rolph l has expressed the opinion that conjugation is a form of 

 nutrition, so that the two conjugating individuals, as it were, devour 

 each other. Cienkowsky 2 also regards conjugation as merely 

 accelerated ' assimilation. There is, however, not only an essential 

 difference but a direct contrast between the processes of conjugation 

 and nutrition. With regard to Cienkowsky 's view, Hensen 3 has 

 well said that ' coalescence in itself cannot be an accelerated nutrition, 

 because even if we admit that both individuals are in want of 

 nourishment, it is impossible that the need can be supplied by this 

 process, unless one of them perishes and is really devoured.' In 

 order that an animal may serve as the food of another, it must 

 perish and must be brought into a fluid form, and finally it must be 

 assimilated. In the case before us, however, two protoplasmic 

 bodies are placed side by side and coalesce, without either of them 

 passing into the liquid state. Two idioplasms unite, together with 

 all the hereditary tendencies contained in them ; but although it is 

 certain that nutrition in the proper sense of the word cannot take 

 place, because neither of the animals receives an addition of liquid 

 food by the coalescence, yet the consequence of this process must 

 be in one respect similar to that of nutrition and growth : the 

 mass of the body and the quantity of the forces contained in it 

 undergo simultaneous increase. It is not inconceivable that effects 

 are by this means rendered possible, which under the peculiar 

 circumstances leading to conjugation, could not have been otherwise 

 produced. 



I believe that this is at any rate the direction in which we shall 

 have to seek for the first meaning of conjugation and for its 



1 Rolph, ' Biologische Probleme.' Leipzig, 1882. 



a Cienkowsky, 'Arch. f. mikr. Anat.,' ix. p. 47. 1873. 



3 Hensen, ' Physiologic der Zeugung,' p. 139. 



