PREFORMATION AND E PI GENESIS 327 



and this is effected through the transmission from generation to gen- 

 eration of a specific substance or idioplasm which we have seen 

 reason to identify with chromatin. This remains true however we 

 may conceive the morphological nature of the idioplasm whether as 

 a microcosm of invisible germs or pangens, as conceived by De Vries, 

 Weismann, and Hertwig, as a storehouse of specific ferments as 

 Driesch suggests, or as complex molecular substance grouped in 

 micellae as in Nageli's hypothesis. It is true, as Verworn insists, 

 that the cytoplasm is essential to inheritance ; for without a specifi- 

 cally organized cytoplasm the nucleus is unable to set up specific 

 forms of synthesis. This objection, which has already been con- 

 sidered from different points of view, both by De Vries and Driesch, 

 disappears as soon as we regard the egg-cytoplasm as itself a product 

 of the nuclear activity ; and it is just here that the general role of the 

 nucleus in metabolism is of such vital importance to the theory of 

 inheritance. If the nucleus be the formative centre of the cell, if 

 nutritive substances be elaborated by or under the influence of the 

 nucleus while they are built into the living fabric, then the specific 

 character of the cytoplasm is determined by that of the nucleus, 

 and the contradiction vanishes. In accepting this view we admit 

 that the cytoplasm of the egg is, in a measure, the substratum of 

 inheritance, but it is so only by virtue of its relation to the nucleus, 

 which is, so to speak, the ultimate court of appeal. The nucleus 

 cannot operate without a cytoplasmic field in which its peculiar 

 powers may come into play ; but this field is created and moulded 

 by itself. Both are necessary to development ; the nucleus alone 

 suffices for the inheritance of specific possibilities of development. 



J. PREFORMATION AND EPIGENESIS. THE UNKNOWN FACTOR IN 



DEVELOPMENT 



We have now arrived at the furthest outposts of cell-research ; and 

 here we find ourselves confronted with the same unsolved problems 

 before which the investigators of evolution have made a halt. For 

 we must now inquire what is the guiding principle of embryological 

 development that correlates its complex phenomena and directs them 

 to a definite end. However we conceive the special mechanism of 

 development, we cannot escape the conclusion that the power behind 

 it is involved in the structure of the germ-plasm inherited from fore- 

 going generations. What is the nature of this structure and how 

 has it been acquired ? To the first of these questions we have as 

 yet no certain answer. The second question is merely the general 

 problem of evolution stated from the standpoint of the cell-theory. 



