412 INTRODUCTION TO CYTOLOGY 



swarm sixties, and nol as the product of the activity of a system of 

 spatially arranged factors in a special germ-plasm. 



In this connection the name of Driesch (1907-8, 1914) has become 

 particularly prominent, not only because of his great experimental ingen- 

 uity, but also because of his decision that the facts of ontogenetic devel- 

 opment cannot be accounted for on the basis of any mechanical theory, 

 either now or in the future. As a result he takes the unscientific step of 

 assuming the existence of a non-mechanical, non-spatial, non-psychic, 

 non-energetic "entelechy," which presides over and controls develop- 

 ment. Such non-experiential agencies, manufactured for the purpose of 

 solving difficult problems, lead to experimental indeterminism and tend 

 only to obscure the points at issue : they may furnish convenient names 

 for great gaps in our knowledge, but they never give more than pseudo- 

 explanations. Nevertheless, in spite of his tendencies to mysticism, as 

 Harper (1919) remarks, Driesch has shown the impossibility of an exact 

 parallelism in spatial configuration between the germ-plasm and the 

 multicellular organism as a whole: there can be no strict preformation 

 in development. On the other hand, the work of the Mendelians shows 

 clearly that development cannot be completely epigenetic: nothing seems 

 clearer than that development is at least in part dependent upon the 

 orderly operation of an internal organization or mechanism. Wilson 

 (1909, pp. 106 ff.), in discussing the relation of the chromatin to heredity 

 and development, writes as follows: 



'But do we really need to employ the pangen symbolism in the consideration 

 of this question? It seems a sufficient basis for our present attack on the problem 

 to assume that the control of the cell-activities is at bottom a chemical one and is 

 effected by soluble substances that may pass from nucleus to protoplasm and 

 from protoplasm to nucleus. Certainly it is to such a view that very many of the 

 chemical and physiological studies in this field are now unmistakably pointing. 

 The opinion is gaining ground that the control of development is fundamentally 

 analogous, perhaps closely similar, to the control of specific forms of physiological 

 action by soluble ferments or enzymes . . . We are thus led to something more 

 than a suspicion that the factors of determination, and therefore of heredity, 

 are at bottom of chemical nature . . . The conclusion thus becomes highly 

 probable that the characteristic differences of metabolism between different 

 species, including those involved in development, are traceable to initial chemical 

 differences in the germ cells. In so far as the chromatin theory expresses the 

 truth, the primary basis of these differences may be sought in the nuclear 

 substance." 



A Chemical Theory of Heredity. — Among the theories based on the 

 conception of the idioplasm as a substance with a special chemical consti- 

 tution, rather than as a system of determinants, may be mentioned that 

 of Adami (1908, 1918). As indicated in Chapter III, Adami attributes 

 the phenomena of life to the activities of a protein-like "biophoric mole- 



