INTRODUCTION 2 1 



These phenomena have only been observed in detail in the 

 higher plants and animals, more particularly in man. In the 

 case of the higher forms of life a large number of facts have 

 now been accumulated which can be used for the purpose of 

 theoretical analysis. 



Although the study of heredity is greatly complicated by 

 amphimixis, this mingling of the hereditary tendencies of two 

 parents, and even the process of sexual reproduction which accom- 

 panies it, afford us a much deeper insight into the actual proc- 

 esses of heredity than we could ever have obtained in any other 

 way. We may thus hope in time to penetrate further into its 

 nature by carrying out more detailed investigations of the phe- 

 nomena. 



In order to do so, however, we must not forget that this form 

 of reproduction is neither the only nor the original one, and that 

 even in multicellular organisms reproduction is not necessarily 

 connected with amphimixis ; it must also be borne in mind 

 that so-called asexual {jnonogonic) reproduction forms the basis 

 of the amphigonic method. The fundamental phenomena of 

 heredity had already shaped their course in the living world 

 before the introduction of amphimixis, and have, therefore, no 

 connection with amphigonic descent and the complications aris- 

 inof from it. This fact has often been overlooked or left out of 

 consideration, and thus the solution of the problem of heredity 

 has been rendered much more difficult. A whole series of the 

 phenomena of heredity can be investigated theoretically without 

 considering the complications arising from amphimixis, though, 

 in point of fact, it is always a factor, and thus the problem to 

 be solved is very considerably simplified. 



The natural course of such an investigation would be to pass 

 from the simple to the complex, but it is not advisable at present 

 to begin the study of heredity by a consideration of the simplest 

 beings, and to ascend from the unicellular to the multicellular 

 organisms. For besides the fact that we know nothing of the 

 individual phenomena, — such as the transmission of the indi- 

 vidual characters, — in the lower forms, the principal reason 

 for not following the ordinary course in this case is the fact 

 that amphigonic reproduction, or the processes of fertilisation 

 and the complicated development of multicellular organisms, 

 affords us, as already stated, a deep insight into the processes 

 of hereditv. The same is true in this case as in almost all 



