OTHER THEORIES OF SPECIES-FORMING. 215 



theories assumed a peculiar vital force, which is not assumed in 

 the later ones, although exception must be made to this statement in 

 favour of the point of view held by the recent so-called neo-Vitalists, 

 those present-day workers who admit the hopelessness of trying to 

 reduce all vital phenomena to a physico-chemical basis. 



An old type of theory of heredity and structure of the germ- 

 plasm, widely held in the seventeenth and eighteenth centuries, is 



Encasement that of the "encasement of the germ" in one of the 

 theory, germ-cells, either the spermatozoid or the egg. The 



essential part of this theory is that the new organism is assumed 

 actually to exist in miniature, with all its parts present, in one of the 

 .germ-cells, and in this miniature body must exist, by repeated encase- 

 ment, all its future progeny. Whether the believer in this theory con- 

 sidered the tiny new creature, only needing to swell and grow to be 

 complete, to be encased in the sperm-cell or the egg-cell, ranked 

 him respectively with the spermatists or the ovalists. A vigorous 

 strife raged between these two factions among the upholders of 

 this simple and effective explanation of heredity which led to cer- 

 tain interesting compromises. A commonly held one was that the 

 sperm-cell furnished the spiritual element, the egg-cell the material 

 and mechanical elements of the new creature. Another, held by 

 Linnaeus, the great botanist and father of biological classification, 

 was that, in plants, the egg (ovule) furnished the internal and re- 

 productive organs, while the sperm-cell (pollen) furnished the exter- 

 nal and vegetative parts. De Candolle, another great botanist, held 

 just the reverse of this view. All these theories of an actual 

 encasement in the germ-cells of a whole or part of a new organism 

 were not mere guesses, but were based on what men thought they 

 saw through their microscopes. The long reign of these theories, 

 now shown to be utterly absurd, illustrates well the constant dan- 

 ger which attends our attempts in all biological study to interpret 

 what we see when working at the limits of visibility. With our 

 much-improved microscopes we laugh at the fantasies which the 

 microscopic vision of our eighteenth-century co-workers raised up. 

 Who may say that our own interpretations of plasm-structure may 

 not seem as absurd to the biologists of the next century? 



By far the great majority of theories of ultimate protoplasmic 

 structure belong to what Delage calls the category of theories of 



Micromeric micromerism. Which means simply that all these 

 theories. theories assume a composition of the plasm out of 



minute ultra-microscopic units of structure, which are also units 

 of life, for all these units are presumed to be endowed with the 

 essential life-attributes. These units may be looked on, as they 

 were by Buffon, as universal, indestructible, hence immortal, parti- 



