AlillFlCIAL Py\.RTHI<:NOGENES[S AND FERTILISATION. 497 



seems to form no hindrance to the normal processes in the 

 egg, and it seems to be of no significance; whether it enters 

 earlier or later into union with one of the descendants of the 

 egg nucleus. The difference between the phenomena of 

 " partial fertilisation " and the normal process is the non- 

 nuion of the nuclei. In certain cases Boveri (1890) 

 described an independent transformation of the nuclei 

 under normal conditions, but the elements from both entered 

 into the equatorial plate of the first cleavage spiadle, and 

 normal division took place. The mere want of union is not 

 of moment; if the sperm nucleus lies near enough the germ 

 nucleus to be influenced by the nuclear fluid of the egg 

 nucleus. The absence of this hastening factor may explain 

 the fact that the karyokinesis of the sperm nucleus in 

 enucleated fragments is much slower than in the cleavage 

 spindle. But such an explanation alone will not hold for 

 cases of dyspermy in these experiments; Avhere the sperm 

 nuclear descendants remain far behind the derivates of the 

 egg nucleuS; and it must be assumed that a change has taken 

 place in the sperm nucleus itself, a kind of paresiS; produced 

 by the potassium hydrate. This holds for the monospermic 

 eggs alsO; and explains wliy, even in spite of its position; the 

 nucleus does not enter into union. 



Another factor is a change in the egg, defined as an over- 

 ripeness. In many cases the germ nucleus is a stage ahead, 

 compared with the normal process, of the centrosome. When 

 the centrosome met the egg nucleus, the latter must already 

 have been in a way prepared for division, and this great 

 readiness to enter into division may be part explanation of 

 the lagging behind of the sperm nucleus. There has not 

 been time for the sperm nucleus to undergo transformation 

 before the egg nucleus has submitted to division. Teichmann 

 does not explain in what the over-ripeness consists. It may 

 perhaps be that, since the eggs had lain fourteen hours in 

 unrenewed sea water, the early preparatory stages of the 

 natural transformation had supervened, which takes place in 

 eggs after lying long in sea water. 



