PROLEGOMENA 



The nucleus with its chromosomes and genetic material is an integral 

 part of the cell which can function only with the rest of the cell, the 

 cytoplasm and its inclusions and structural parts. The cytoplasm, in 

 contrast, differentiates in development, performs the physiological 

 functions of life, is involved in the processes of growth, movements 

 and shifts, interrelations with neighboring cells, and all the mor- 

 phological and physiological features which constitute development 

 and differentiation. The facts of genetics prove that all these features 

 of the cytoplasm (i.e., of the cell as a whole) are under the control 

 of the genie material in the nucleus. In such extreme cases as somatic 

 mosaics involving single cells, in which the chromosomal constitution 

 has been changed by elimination of whole chromosomes or parts 

 thereof or by somatic crossing over, the genie control of chemical 

 (pigment) or morphological (e.g., bristles) traits can be seen within 

 a single cell. Thus we are confronted with the problem of the inter- 

 relations between genie material in the chromosomes and the efiFective 

 parts of the cell, the cytoplasm in the broadest sense. 



Among these interrelations, the first place is occupied by the 

 removal of the primary products of the genie material from the 

 nucleus into the cytoplasm, the place of their action; and, vice versa, 

 by the entry of the raw materials for nuclear growth and duplication 

 from the cytoplasm. The study of these relations is basic in develop- 

 mental or physiological genetics dealing with the actions of the genie 

 material in controlling development. 



In the present chapter, the cytoplasm enters only as substrate in 

 a broad sense, which includes the specificity of its matter and struc- 

 ture, some parts of which may be just the expression of actual 

 continuity with the ancestral plasms, while other features may be the 

 product of genie action in the original egg cell. We might call the 

 cytoplasmic specificity its hereditary constitution, meaning no more 

 than the fact that the cytoplasm of a fly or lily cell is continuous with 

 the cytoplasm of the ancestral cells and, in this general way, speak of 

 cytoplasmic heredity. (We shall see, below, that this phenomenon 

 exists.) It will then be necessary to separate such ancestral, direct 

 specificity of the cytoplasm from a specificity which already is estab- 

 lished in the unfertilized egg under genie control, as can be verified 

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