20 THE GERM-PLASM 



alone in considering all living matter to be actually composed 

 of his ' pangenes/ though I have already indicated that my 

 ' ancestral germ-plasms ' are also composed of similar primary 

 units, which do not exist in them alone. The minute vital 

 particles or ' plasomes,' adopted by Wiesner from Briicke. cor- 

 respond in all essential points to the • biophors ' or bearers of 

 life assumed by myself. 



B. — Descriptive Part 



By the term heredity is simply meant the well-known fact 

 that living organisms are able to produce their like, and that the 

 resemblance between a child and its parent, although never 

 perfect, may nevertheless extend to the most minute details of 

 construction and functions. 



The fundamental phenomena of heredity are familiar in all 

 existing organisms : the transmission of the character of the 

 species from parent to offspring results whether the multiplica- 

 tion takes place by the halving of a unicellular organism or by 

 the process which occurs in multicellular organisms, which 

 consists in a complex succession of continually increasing 

 groups of cells, i.e., in development. These fundamental phe- 

 nomena of heredity are, however, complicated in all the higher 

 organisms by the connection of reproduction with that process 

 which may be described as amphimixis.* This consists in the 

 mingling of two individuals or of their germs, and owing to its 

 constant connection with reproduction in multicellular organisms 

 it is usually spoken of as ^sexual reproduction.' As will be 

 shown in greater detail further on, the various phenomena, such 

 as the blending of parental characters in the offspring, and 

 reversion, depend exclusively on the hold which amphimixis has 

 taken on the life of the species. Similar phenomena must occur 

 amongst unicellular organisms, in which amphimixis is widely 

 spread if not universal, in the form of conjugation, and is, 

 therefore, not directly connected with reproduction. At present, 

 however, we are ignorant of the details of heredity in these 

 forms, and are therefore compelled to base our conclusions 

 entirely upon what we know to occur in multicellular organisms. 



* August Weismann, 'Amphimixis, oder die Vermischung der In- 

 dividuen,' Jena, 1891. See ' Essays upon Heredity,' vol. ii,, 1892. 



