v.] IN THE THEORY OF NATURAL SELECTION. 293 



sumption, which is also incapable of proof, that a smaller 

 amount of reproductive force is required for the development 

 of a male individual than for the development of a female. It is 

 true that the unfertilized eggs of the bee produce male indivi- 

 duals, while the fertilized ones develope into females, but in 

 certain other species the converse association holds good, while 

 in others, again, fertilization bears no relation to the sex of the 

 offspring. 



Although the mere fact that parthenogenesis occurs at all is, 

 in my opinion, sufficient to disprove the theory of rejuvenes- 

 cence, it is well to remember that parthenogenesis is now the 

 only method of reproduction in many species (although we do 

 not know the period of time over which these conditions have 

 extended), and is nevertheless 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^ has expressed the opinion that conjugation is a form 

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

 devour each other. Cienkowsky^ 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 Cien- 

 kowsky's view, Hensen'^ 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 impos- 

 sible that the need can be supplied by this process, unless one 

 of them perishes and is really devouffed.' 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 assi- 

 milated. 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, 



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



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



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



