EFFECTS OF AMPHIMIXIS ON ONTOGENY 253 



CHAPTER IX 



ONTOGENY RESULTING FROM THE UNION OF 

 THE GERM-PLASM OF TWO PARENTS 



I. The Nature of the Offspring Determined by the 



Process of Fertilisation 



The first question which presents itself in the consideration of 

 ' amphigonic heredity ' is concerned with the relative share taken 

 by the germ-plasm of each parent in the control of ontogeny : — 

 whether the paternal and maternal ids always co-operate simul- 

 taneously, and the forces contained within them together form a 

 single resultant, or whether one group only is active while the 

 other remains passive. This question cannot at present be de- 

 cided from the results of observations on the nuclear substances 

 themselves ; the phenomena of heredity, together with what we 

 know concerning the composition of the idioplasm resulting 

 from amphimixis, can alone help to elucidate this problem. 

 These phenomena must therefore be analysed as accurately and 

 minutely as possible. 



We must base our analysis on the fact which we have already 

 proved, that the germ-cells of an individual differ from one 

 another as regards the hereditary substance they contain, and 

 that the proportion of paternal and maternal ids in a germ-cell 

 varies between wide limits, the degree of variability being greatly 

 increased by the union of the germ-cells of two individuals in 

 the process of amphimixis. This fact is sufficient to account for 

 the difference existing in the human race between children of the 

 same parents. The fundamental law of amphigonic heredity 

 enunciated by Victor Hensen follows directly from this fact : — 

 '•the individual is deter )nined at the tivie of fertilisation ; ' or, in 

 other words, the individuality of an organism results from the 

 fact that the germ-plasm is composed of the paternal and maternal 

 ids which are brought together in the egg-cell. 



This law is not self-evident, for we might have believed, a priori^ 

 that the development and mingling of parental characters in 

 the offspring is due entirely, or at any rate to a great extent, to 



