16 Vitality and Organization of Protoplasm. 



this hypothesis of ontogenetic evolution, starting from the cell-theory, 

 ends by refuting it. 



Mechanico-'physioJogical Theory — Na-egeli. 



In 1884 Naegeli published his elaborate "Mechanico-physiological 

 Theory of Evolution." In this important work he also adopts the cell- 

 theory, of which he was one of the principal originators. It underlies 

 his explanation of phylogenetic and ontogenetic phenomena. Taking 

 thus the multicellular organism to be an aggregate of unicellular or- 

 ganisms, the lineal offspring of an initial parent-cell, the question here 

 again arises : First, as to the means by which the successive generations 

 of daughter-cells constituting the multicellular organism have become 

 differentiated in its divers, highly developed tissues? and second, hoAV 

 these widely differentiated cellular beings come to be as such potentially 

 represented in the reproductive germ-cell of higher organism? 



To answer these fundamental biological questions, ISTaegeli assumes 

 the existence of a gradually developed germinal substance, which he 

 calls "idioplasm." This reproductive substance he endows with an in- 

 trinsic tendency to undergo phyletic development, and also with the 

 capability of being to some extent structurally and functionally influ- 

 enced by external conditions; and he believes that it is the intrinsically 

 originated and directed process of development which leads to phyletic 

 evolution, whilst the external influences bring about adaptation to the 

 environment. 



The idioplasm or germinal substance is conceived by jSTaegeli as 

 being segregated from plasm composed of micellae, which elementary 

 bodies he holds to be invisibly small organic crystals surrounded by a 

 watery film. Primordially, micellae are said to arise spontaneously in 

 albuminous solutions. Whereupon by force of their molecular activi- 

 ties they arrange themselves into groups, which grow by intussusception 

 of newly formed micellae, and then, as such, multiply by self-division. 

 Through summation of the molecular forces of groups, whose micellae 

 are similarly oriented, molar forces come into play, that initiate new 

 chemical processes, by which specific plastic tissue-products are phylet- 

 ically formed. And these being influenced in their formation, not only 

 intrinsically, but also by external stimuli, are found to be adapted to 

 their medium. 



It is in this way that in the -course of phyletic evolution groups of 

 idioplasmic micellae become more and more differentiated, so as to con- 

 stitute respectively the "Anlage" or germ of the variform cell-structures 

 composing the com])lex organism. The idioplasm of the germ-cell of 

 a multicellular organism consists, therefore, of as many divers idio- 

 plastic germs, or differentiated groups of micellae, as there are differen- 

 tiated cells in the adult organism to be reproduced therefrom, and these 

 are reproduced in the order in which the pliyletic development of the 

 specific groups of micellae has taken place. 



The germinal potency of the idioplasm is. l)y moans of growth and 



