174 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



We know little at present about the detail of processes going 

 on in the cell, and mediating between nucleus and cell-body 

 and between this latter and the centrosoma ; but I believe that 

 this at any rate may be regarded as certain, viz. that everything 

 which occurs in the cell, including the rhythm and the manner 

 of its multiplication, depends upon the nuclear substance. But 

 if this be so we cannot neglect its quantity : there must be a 

 minimum amount of tiudear substance below which the control over 

 the vital processes of the cell cannot be completely exercised. If this 

 be correct, we shall be justified in explaining the cases of excep- 

 tional parthenogenesis by the assumption, that the nucleoplasm 

 of certain eggs possesses a greater power of growth than that 

 of the majority of eggs of the same species ; while in the case 

 of the bee, every ovum possesses a power of growth sufficient 

 to double its nuclear substance, after reduction to half,— that is, 

 when it is not raised to the full amount by means of fertilization. 



This explanation, so far as I can see, is in complete agree- 

 ment with all the facts of the case, and especially with the 

 observations by which various investigators were, in earlier 

 times, enabled to show that the unfertilized eggs of various 

 species of animals, e.g. the silk-worm moth {Bombyx mori), 

 frequently enter upon an embryonic development which is never 

 completed, but is arrested at an earlier or later stage. This 

 becomes intelligible if we suppose that the cell is controlled by 

 the quantity of nucleoplasm. According as the germ-plasm, 

 diminished to half by expulsion of the two polar bodies, 

 possesses a weaker or stronger power of growth, it will 

 follow that its quantity will be sufficient to bring about the 

 first divisions of the ovum, but not to complete the whole em- 



zoon divide during fertilization, and that the halves fuse together to form 

 the two pole-bodies of the first segmentation spindle, agrees well with 

 this view. Fol, ' La Quadrille des Centres,' Geneve, 1891. Moreover 

 this observation does not include anything which need surprise us, 

 because nothing takes place except that which precedes every nuclear 

 division, viz. the doubling of the centrosoma. The two sexual nuclei 

 behave exactly like any other nuclei : even as regards outward appear- 

 ance they may retain their independence for a long time in certain 

 species, and fusion into a single nucleus only occurs at a later stage of 

 segmentation. The evidence for this statement is afforded by observa- 

 tions upon Cydopidae by Dr. Ischikawa, communicated to me in letters, 

 and independently by the researches of my assistant, Dr. Hacker, upon 

 the same animals. 



