192 GEOLOGICAL BIOLOGY. 



nency is only relative; that, somehow, the higher characters 

 become modified as well as the lower. Thus it is supposed 

 that by such gradual modification, taking place in the course 

 of genealogical descent, successive individuals arise which 

 differ specifically from their ancestors, later others which at- 

 tain generic difference, and after a great many generations 

 the family characters are changed ; and still later they differ 

 ordinally, and, theoretically, even such radical differences of 

 structure as distinguish one class from another may be thus 

 attained. 



Fixed Characters those which are Transmitted Unchanged in 

 Natural Descent. — In ordinary natural development, or onto- 

 genesis, there is a law of constancy regarding all the charac- 

 ters expressed by the symbols B 6, C 2, etc., to S 115. These 

 may be then called the fixed characters of the species at any 

 particular time, and be indicated by the letter M. But, as 

 we have explained, in the course of time among the de- 

 scendants may appear a new genus, G 1 1 ; the point of geo- 

 logical time, or the stage in the history, marking such an 

 event is when the new species assumes dominance in indi- 

 viduals, and the old forms drop out, and leave a gap in the 

 series. The species M may be considered as expanding at 

 this point to include new generic characters, or we may con- 

 sider the new genus as arising as an offset from the old 

 forms. It will be seen that all the individuals possessing the 

 characters M form a common race, and that divergence of 

 race proceeds from varietal, through specific, generic, family, 

 etc., characters, and in the order here given; and that the 

 series, branch, class, order, etc., are expressive of the natural 

 order in rank of importance of the characters, in their an- 

 tiquity, and in their fixity. 



Rank of Characters, the Precision of their Reproduction, and 

 their Antiquity. — If we arrange the characters in the inverse 

 order, thus: V, S, G, F, etc., we have expressed the char- 

 acters in the order of their increasing importance, increasing 

 fixity, and constancy of their repetition by generation. 

 There is thus seen to be a law of relation existing between 

 the certainty and accuracy of repetition in reproduction, and 

 the number of times the reproduction cycle has been re- 



