44 EMBRYOLOGY. 



latter of which has come close up to the former, without, however, 

 fusing with it. A union of the male and female nuclear substances 

 into a common nuclear figure takes place in the case of the Maw- 

 worm, when the process of egg-cleavage is beginning. 



The processes of fertilisation just described can be designated as 

 typical for the animal kingdom. But they appear to recur in exactly 

 the same manner throughout the vegetable kingdom also, as has 

 been shown by the thorough investigations of STEASBURGEK. We 

 are therefore in a better position now than formerly to advance a 

 theory of fertilisation based upon an important array of facts : 



In fertilisation clearly demonstrable morphological processes take 

 place. Of these the important and essential one is tJie union of two 

 cell-nuclei which have arisen from different sexual cells, a female egg- 

 nucleus and a male spermatic nucleus. These contain the fructifying 

 nuclear substance, which is an organised body and comes into activity 

 as such in fertilisation. 



Recently the attempt has been made to expand the fertilisation 

 theory into a theory of transmission. Important reasons may be urged, 

 as appearing to indicate that the fructifying substance is at the 

 same time the bearer of the transmissible peculiarities. The female 

 nuclear substance transmits the peculiarities of the mother, the male 

 nuclear substance the peculiarities of the father, to the nascent creature. 

 Perhaps there is in this theory a morphological basis for the fact 

 that offspring resemble both progenitors, and in general inherit from 

 both equally numerous peculiarities. 



If we accept these two theories, the nucleus, which, despite its 

 constant presence, previously had to be described as a problematic 

 structure of unknown significance, acquires an important role in the 

 life of the cell. It seems to be the cell's especial organ of fertilisation 

 and transmission, inasmuch as there is stored within it a substance 

 (idioplasma of NAGELI) which is less subject to cell metastasis. 



In connection with the consideration of the process of fertilisation 

 may be permitted a slight digression to the realm of pathological 

 phenomena. 



As follows from numerous observations in both the animal and 

 vegetable kingdoms, in the normal course of fecundation only a single 

 spermatic filament penetrates into an egg, when the encountering 

 sexual cells are entirely healthy. But with an impaired condition of 

 the egg-cell, superfetation by means of two or more seminal filaments 

 (polyspermia) takes place. 



Superfetation may be produced artificially, if by way of experiment 



