130 ORGANISM AND MECHANISM 



threads composing the skeleton of the common bath sponge, 

 largo numbers of secretory cells called l spongoblasts ' group 

 themselves in double file every here and there through- 

 out the middle stratum of the sponge, as if some unseen 

 captain marshalled them. Up the middle of the double file 

 the spongin is secreted, made at the expense of the living 

 matter of the spongoblasts, and the many individual contri- 

 butions coalesce into a spongin-fibre. 



In his Science and Philosophy of the Organism (1908), 

 Driesch has with unexampled thoroughness and subtlety 

 tested the possibilities of mechanistic description with 

 particular reference to the facts of development. He reaches 

 a conclusion of the first importance : " No kind of causality 

 based upon the constellations of single physical and chemical 

 acts can account for organic individual development; this 

 development is not to be explained by any hypothesis about 

 configuration of physical and chemical agents. . . . Life, 

 at least morphogenesis, is not a specialised arrangement 

 of inorganic events; biology, therefore, is not applied 

 physics and chemistry; life is something apart, and bi- 

 ology is an independent science." But what, it may be said, 

 of the science of ' developmental mechanics ' and of the 

 lengthening row of volumes entitled Archiv fur Entwick- 

 lungsmechanik? The first answer is, that, after all, the 

 developing embryo is a material system, and must exhibit 

 chemical and physical means. Development shows a continu- 

 ous action and reaction between an implicit organisation and 

 the environing conditions, and * developmental mechanics ' 

 so-called is in great part concerned with discovering the 

 correlation between steps in development and their ap- 

 propriate external stimulation and nurture. These cor- 

 relations are of great interest, but as our knowledge of them 



