356 V. THE NATURE OF EVOLUTION 



Others according to the general property of protein concerning memory 

 and forgetting. The change will be continued until the differentiated 

 structure is recovered from which the primitiv^e structure of the germ 

 cell was induced, thus the reversible change of the germ cell to the 

 somatic being established. 



Now, we have to consider this problem in connection with genes. 

 Since protoplasm structure is controlled by genes, the change of the 

 former should be involved in the change of the latter. It may be 

 said, therefore, that genes are changed during ontogeny in every direc- 

 tion according to the various parts, or organs, of the body, so that 

 every organ or tissue in a fully developed individual must have its 

 own specific genes. 



This conclusion may seem unreasonable to the majority of authors 

 who believe firmly that genes are never changed except by mutation. 

 Nevertheless, the evidences strongly suggesting the ununiformity of 

 genes among various organs even in one and the same individual have 

 generally been known. Namely, on the one hand, the immunological 

 fact that organs have their antigenic specificity, that is, that organs 

 contain their own specific proteins is well known ; whereas, on the 

 other hand, it is generally accepted that the protein structure in a cell 

 is governed by the genes. It should naturally follow from these two 

 facts that cells of every organ and tissue share their specific genes, 

 never similar to each other. 



The necessity of stressing the importance of chromosomes in the 

 organization of plants and animlas,. and their decisive role in inherit- 

 ance, caused O. Hertwig in 1918 to formulate the "Law of constancy 

 of chromosome number" which implies that all cells of a given organ- 

 ism contain the same somatic number of chromosomes. A great num- 

 ber of observers have, however, shown that his concept is in need of 

 revision. Especially in insects and in plants, it has been established 

 that certain cells and even whole tissues may represent different de- 

 grees of polyploidy. It has been found that a similar variation occurs 

 also in the somatic chromosome number of man (31). This may be re- 

 garded as another evidence indicating the ununiformity of genes. 



Thus it may be said that ontogeny is a phenomenon brought about 

 by a complicated change of the gene in the germ cell, as is illustrated 

 diagrammatically in Fig 34. In this diagram, A represents the gene 

 or the gene-complex in the germ cell. A' and A" the genes in somatic 

 cells developed from the germ cell, and A'" the gene of the mother 

 germ cell developed also from the germ cell. 



A can be converted to A', A" and A'" respectively, by the action 

 of the environmental factors, a', a" and a'". A'" has the property to 

 be readily reduced to A by the effect of x. Also between A'" and A' 



