94 REMARKS ON CERTAIN [XI. 



by so many writers, particularly by Kolliker ^, now appears to be 

 justified. If the nucleus of a spermatozoon is capable of con- 

 veying to the body of an ovum which has lost its nucleus, the 

 hereditary tendencies contained in itself, and of producing an 

 organism with paternal characters only, — then we can scarcely 

 conceive of ontogeny except as a series of regular changes of 

 the idioplasm, advancing from cell-division to cell-division, 

 and giving its special character to the body of every cell at 

 every stage of growth, not only in respect to form, but also to 

 function, and especially with regard to the rhythm of cell- 

 division. 



Professor Vines raises a further objection against my views on 

 the origin of variation. In the fifth essay ^ I looked for the signi- 

 ficance of sexual reproduction in the fact that it alone could 

 have called forth that multiplicity of form which is met with 

 among the higher plants and animals, and that constantly 

 varying combination of individual variations, which natural 

 selection required for the creation of new species. I still hold 

 to the view that the origin of sexual reproduction in reality 

 depends on the assistance which it affords to the working of 

 natural selection, and I am entirely convinced that the higher 

 development of the organic world was only rendered possible 

 by the introduction of sexual reproduction. On the other hand, 

 I am inclined to believe that Professor Vines is right in his 

 contention that sexual reproduction is not the only factor which 

 maintains the variability of the Metazoa and Metaphyta. I 

 might have pointed out in the English translation of my essays 

 that my views on this point had somewhat altered since the 

 appearance of the German originals. My lamented friend. 

 Professor De Bary, too early lost to science, had already 

 directed my attention to those fungi which propagate them- 

 selves parthenogenetically, and which Professor Vines justly 

 cites against this part of my view ; but I wished on the grounds 

 mentioned above to make no alteration in the essays. At the 

 time when I wrote the essay in question (1886), I was well 

 aware that my views on the causes of individual variation were 



' Kolliker, ' Das Karyoplasma und die Vererbung : eine Kritik der 

 Weismann'schen Theorie von der Kontinuitat des Keimplasmas.' Z. f. 

 W. Z. Bd 44, p 228, 1886. 



^ See Vol. 1, p. 257. 



