THE GERM-PLASM 75 



state of the brain during sleep, or of the latent period of certain 

 fertilised animal eggs, which, after beginning to undergo develop- 

 ment, remain inactive at a certain stage for months. The facts 

 with which we are acquainted, however, render the assumption 

 of an active and an inactive state of the ids and determinants 

 unavoidable, as will become more evident in the course of this 

 book. A similar assumption has been made by all those who 

 have formulated vital units : thus Darwin has assumed these 

 conditions in connection with his 'gemmules,' and de Vries with 

 regard to his ' pangenes.' 



Two forms of ]ieredity, which we call homotopic and homo- 

 chronic, may be deduced from the theory given above. As 

 the individual determinants — from the germ-plasm onwards, 

 throughout all the stages of ontogeny — take up a definite posi- 

 tion in the id. they must reach the right place in the body, and 

 there cause the development of a structure corresponding to 

 that of the parent. As, moreover, the period of maturation of 

 each determinant is decided by the nature of the latter, the 

 determinant will become active in the individual and will cause 

 the formation of any particular part of the body at the same 

 stage of development as in the parent. Exceptions to this rule 

 occur in the case of abnormalities, and also in that of phvlo- 

 genetic displacements. 



5. Summary of Sections 1-4, relating to the Structure 

 OF the Germ-plasm 



According to my view, the germ-plasm of multicellular organ- 

 isms is composed of ancestral germ-plasms or ids, — the vital 

 units of the third order, — each nuclear rod or ida7it being 

 formed of a number of these. Each id in the germ-plasm is built 

 up of thousands or hundreds of thousands of determinants. ■ — tlie 

 vital units of the second order, — which, in their turn, are com- 

 posed of the actual bearers of vitality (• Lebenstrager '), or dio- 

 phors, — the ultimate vital units. The biophors are of various 

 kinds, and each kind corresponds to a different part of a cell : 

 they are, therefore, the • bearers of the characters or qualities ' 

 (" Eigenschaftstrager ') of cells. Various but perfectly definite 

 numbers and combinations of these form tlie determinants, each 

 of which is the primary constituent ('Anlage') of a particular 



