HOMOLOGY AND ITS INTERPRETATION 41 



ity. Variation by diverting old currents into new channels 

 adjust organisms to new situations and brings about modifica- 

 tion. Homology, therefore, is the effect of inheritance, while 

 adaptedness or modification is the product of variation. 



As here used, the term inheritance denotes something more 

 than a mere recurrence of parental characters in the off- 

 spring. It signifies a process of genuine transmission from 

 generation to generation. Strictly speaking, it is not the char- 

 acters, such as coloration, shape, size, chemical composition, 

 structural type, and functional specificity, that are ''inherited," 

 but rather the hereditary factors or chromosomal genes, which 

 are actually transmitted, and of which the characters are but 

 an external expression or manifestation. Hence, it is scarcely 

 accurate to speak of "inherited," as distinguished from ''ac- 

 quired," characters. As a matter of fact, all somatic charac- 

 ters are joint products of the interaction of germinal 

 and environmental factors. Consequently, the external char- 

 acter would be affected no less by a change in the envi- 

 ronmental factors than by a change in the germinal factors. 

 In a word, somatic characters are not the exclusive expression 

 of the genetic factors, but are equally dependent upon environ- 

 mental influence, and hence it is only to the extent that these 

 characters are indicative of the specific constitution of the 

 germ plasm that we may speak of them as "inherited," remem- 

 bering that what is really transmitted to the offspring is a 

 complex of genes or germinal factors, and not the characters 

 themselves. The sense is, therefore, that "inherited" char- 

 acters are manifestative of what is contained in the germ 

 plasm, whereas "acquired" characters have no specific germ- 

 inal basis, but are a resultant of the interaction between 

 the somatic cells and the environment. In modern termin- 

 ology, as we have seen, the aggregate of germinal factors 

 transmitted in the process of reproduction is called the 

 genotype, while the aggregate of somatic characters which 

 manifest these germinal factors externally is spoken of as the 

 phenotype. Only the genotype is transmitted, the phenotype 



