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THE AMERICAN NATURALIST [Vol. XLV 



of living substance — hereditary substance or idioplasm, 

 and 'nutritive substance' or troplioplasm, and tbat the 

 former is much smaller in amount than the latter" (Weis- 

 mann, '04, Vol. I, p. 341). The idioplasm of the germ 

 cells he calls genu plasm, a substance which is "never 

 formed de novo, but it grows and increases ceaselessly; 

 it is handed on from one generation to another like a long 

 root creeping through the earth, from which at regular 

 distances shoots grow up and become plants, the indi- 

 viduals of the successive generations" (Vol. I, p. 416). 

 "This splitting up of the substance of the ovum into a 

 somatic half, which directs the development of the indi- 

 vidual, and a propagative half which reaches the germ 

 cells and there remains inactive, and later gives rise to 

 the succeeding generation, constitutes the theory of the 

 continuity of the germ plasm (Vol. I, p. 411). Accord- 

 ing to this theory, the body or somatic cells serve only to 

 protect, nourish and transport the germ cells which con- 

 tain the germ plasm. Later the germ cells separate from 

 the body and develop into new individuals and the body 

 subsequently dies. 



In the eggs of chrysomelid beetles the germ cells are 

 formed at an extremely early period in embryonic devel- 

 opment. They separate entirely from the embryo and 

 come to lie in a group at the posterior end; at this time 

 germ cells are quite distinct from somatic cells. Later 

 the germ cells migrate back into the embryo, where they 

 are protected, nourished and transported until they be- 

 come mature, leave the body and give rise to a new gen- 

 eration. 



What particular part of the germ cell represents the 

 idioplasm or germ plasm ? is a question of fundamental 

 importance. Weisniann recognizes the chromosomes as 

 the germ plasm and has built up a complex theory as to 

 the constituents of these bodies. The present discussion 

 is not concerned in any way with the structure of the 

 germ plasm as conceived by Weismann, and the writer 

 does not wish to become involved in a consideration of 

 idants, ids, determinants and biophores. The theory of 

 dichromaticity (Dobell, '09) may aid in answering this 



