INTRODUCTION 35 



Hereditary substance^ in the full meaning of the term — i.e.^ 

 that substance which contains all the primary constituents 

 of the whole organism, is merely the idioplasm of the germ-' 

 cell, and it is advisable for practical purposes to denote 

 this first onto-idic stage by the short term genn-piasui, which I 

 suggested for it at a time when the idea of idioplasm had not 

 been introduced. At that time I meant bv the term 'germ- 

 plasm ' the hereditary substance of a germ-cell capable of 

 development, without expressing any opinion as to its position 

 or nature. We can now state that the germ-plasm is the first 

 ontogenetic stage of the idioplasm of an animal or a plant, 

 whether the cell, in the nucleus of which it is contained, is 

 sexually diflferentiated or not. 



We must next attempt to form an idea of the constittition and 

 nature of the germ-plas?n, and of the ontogenetic stages of the 

 idioplasm, or onto-idic stages. 



