150 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



different routes, which however always meet at the principal 

 stations, viz. the two nuclear divisions. We have learnt two 

 of these routes, on the one hand from O. Hertwig, on the other 

 from Henking : the observations of Flemming on the formation 

 of spermatozoa in the salamander may possibly point to a 

 third, those of Hacker to a fourth, but all agree in leading to 

 the same end. 



II. Inheritance in Parthenogenetic Reproduction. 



The Processes of Maturation in Parthenogenetic Eggs and their 



Meaning. 



It has for some years been recognized that the characteristic 

 development of an egg into a fully formed individual is chiefly 

 dependent on the nuclear substance, in so far as it is this which 

 compels distinct differentiation in a cell-body which was pre- 

 viously, at any rate to some extent, indifferent, and which 

 communicates to the total product of the egg-cell distinct 

 modes of multiplication and development. When this became 

 known it was obvious that the amount of nuclear substance 

 possessed some significance, and that a certain mass of it was 

 essential for the commencement of embryogeny in an egg-cell. 

 I have therefore for some time agreed with Strasburger in 

 seeking for the power of development without fertilization 

 possessed by many ova, in the assumption that they contain an 

 amount of germ-plasm which is twice as great as that present 

 in eggs requiring fertilization, or that they can give rise to this 

 amount by means of some process of growth. When the proof 

 was afterwards afforded that parthenogenetic eggs produce 

 only one polar body instead of two, I concluded, as is men- 

 tioned above, that the formation of the second polar body alone 

 signified the halving of the number of ids which was required 

 by the theor}^ ; for we could not assume that such a halving 

 took place in parthenogenetic eggs. I looked upon the first 

 halving of the nuclear substance, common to both kinds of 

 eggs, as the removal of some nuclear substance which had no 

 further use in either case, and the omission of the second 

 nuclear division in parthenogenetic eggs I regarded as the 

 means for retaining the amount of germ-plasm necessary for 

 the egg to complete its course of embryogeny. 



