208 The Unity of the Organism 



tity of the parts, Born interprets as supporting the mosaic 

 theory. He says : "From our beginning stage on, the de- 

 velopment rests essentially upon self-differentiation of the 

 particular (einzelnen) parts a correlative influence of the 

 neighborhood (Nachbarshaft) as of the whole cannot be 

 recognized — neither negative nor positive ; the development 

 therefore corresponds throughout from our beginning stage 

 on to the mosaic theory of Roux. The organ-forming germ 

 regions are parceled out (His)." ^^ 



That an individual plant or animal made up of parts of 

 the bodies of two or more other plants or animals grown 

 together, each constituent maintaining its identity wholly 

 unmodified by the other parts, has as much resemblance 

 to a mosaic picture as can well be imagined for any living 

 being, must be granted. No one should, however, fail to 

 see the difference between a mosaic of this sort and one of 

 the sort conceived on the basis of the developmental facts 

 which were the starting point of Roux's theory. In the first 

 place "mosaic pictures" of the kind produced by grafting 

 are genuinely man-made affairs. They never occur in na- 

 ture. A "mosaic theory" contributes nothing substantial 

 to their interpretation. Indeed it is difficult to see that 

 there is room here for any such tlieory. Such a composite 

 creature undoubtedly resembles somewhat a mosaic picture 

 and that would seem to be all there is to it. But undoubted- 

 ly such a creature also differs very much from a mosaic pic- 

 ture. For one thing, the creatures are alive and mosaic 

 pictures are not. However, I have no wish to make all that 

 might be made against the mosaic theory because of its higli 

 degree of artificiality. The main purpose in bringing for- 

 ward Born's work and ideas at this point is to direct atten- 

 tion to his proposal touching what might be called the 

 scientific aspect of the mosaic theory. The organ-forming 

 germ areas (organbildende Keimbezirke) of His to which 

 Born refers, and which unquestionably played a large part 



