l6o AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



adaptation of a species to new conditions of life \ I argued that, 

 the repeated minghng of two individualities being requisite to 

 supply the process of selection with the necessary choice of 

 combinations of individual qualities, — it follows that a choice 

 of sufficient range will not be supplied when one and the same 

 set of combinations are passed on by parthenogenesis, through 

 long series of generations, to an ever increasing number 

 of individuals. A number of ' identical ' individuals would 

 thus arise, that is individuals which contain a precisely 

 similar fundamental stock of hereditary predispositions, and 

 which, at most, can only be distinguished by transient pecu- 

 liarities, viz. by those which are the consequence of external 

 influences of various kinds upon the body during its pro- 

 gress towards maturity or after maturity has been reached. 

 When writing on this subject, I expressed the opinion that 

 ' all species with purely parthenogenetic reproduction are sure 

 to die out ; not, indeed, because of any failure in meeting the 

 existing conditions of life, but because they are incapable of 

 transforming themselves into new species, or, in fact, of 

 adapting themselves to any new conditions-.' I stated this 

 conclusion in the strongest possible way although I thought 

 that it might perhaps require subsequent modification, because, 

 even at that time, I had already considered the possibility that 

 the consequences of sexual reproduction of ancestors might 

 affect their purely parthenogenetic descendants. But whether 

 a simple rearrangement of the ids within the idants would 

 suffice to call forth a fresh combination of individual peculiar- 

 ities, appeared to me very doubtful ; and 3^et this would have 

 been the only alteration in the germ-plasm which we could 

 have been led to suggest by the state of our knowledge at the 

 time ; for a ' reducing division ' could not have been supposed 

 to take place in parthenogenetic eggs, because we did not know 

 that the number of the idants doubles before the occurrence ot 

 the first polar division, and because a halving of the number 

 of idants, without any previous doubling, would necessarily, 

 in a few generations, diminish their number to one. But now 

 the case is different, and we may affirm that in parthenogenetic 



^ * Die Bedeutung der sexuellen Fortpflanzung.' Jena, 1886, p. 58. 

 Translated as the fifth essay. See Vol. I. p. 298. 

 2 See Vol. I. p. 298. 



