PART III 



THE PHENOMENA OF HEREDITY RESULTING 

 FROM SEXUAL REPRODUCTION 



Introductory Remarks on the Nature of Sexual 

 Reproduction. 



The phenomena of heredity have so far been considered in 

 connection with a purely asexual form of reproduction only : the 

 complications of the germ-plasm arising from the intermingling 

 of the hereditary parts of two parents have been left aside, and 

 the composition of the germ-plasm has been assumed to be of 

 such a nature as would result if 7no7iogonic reproduction were 

 the only form in which the process existed. The advantage of 

 this method of procedure is seen in the fact that it has only been 

 necessary for us to bear the essential part of the processes in 

 mind when analysing the fundamental phenomena of heredity, 

 and this essential part has therefore not been lost sight of in the 

 confusing and ever changing intermixture of individual variations 

 which result from amphigonic reproduction. The course we 

 have followed is justified by the fact that fundamental processes 

 — such as ontogeny, regeneration, and multiplication by fission 

 and gemmation — cannot owe their origin to amphigonic repro- 

 duction, but would take place even if this form of multiplication 

 did not exist at all. 



Bearing this fact in mind when considering the complications 

 arising from sexual reproduction with which we have to deal 

 in analysing the phenomena of heredity and their material sub- 

 stratum, it will now be profitable to consider the facts concerning 

 this form of reproduction, and to see how they can be explained. 

 I will now therefore give a short account of the processes in 

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