442 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



tion that SA -f- ga l represents the first of a line in which 

 a given character appears). A new character or an 

 additional increment of the same character, appears 

 in the second stage of acceleration "2," and is repre- 

 sented as before, by Aa~, the A appearing in the soma, 

 and the a- being added to the character of the germ- 

 plasma. In the third stage, the new character a 2 ap- 

 pears in the soma, which now becomes Sa l a 2 . The a- 

 acquired by the germ-plasma of the second stage, is 

 inherited by that of the third, which is therefore rep- 

 resented by g^a 2 }. To the third stage is now added 

 the acquisition Aa*. The a B is again incorporated into 

 the soma of the succeeding or fourth stage, which is 

 therefore represented by the expression Sa l a 2 a 3 ; while 

 the germ-plasma of the same (fourth, "4,") stage, is 

 represented by g^a-a 3 ), and so on. The lines of im- 

 mediate inheritance are represented by straight lines. 

 The vertical lines represent the descent of characters 

 from one type of the germ-plasma to a succeeding 

 one ; and the oblique lines represent the transmission 

 of the same characters to the soma into which it grows, 

 as the succeeding generation or stage. 



The letters a 1 , a 2 , etc., expressive of characters ac- 

 quired by the germ-plasma, are numbered for identifi- 

 cation only. Should the influences derived from the 

 ancestry of the other sex be added to the diagram its 

 complexity would become inconvenient, and they are 

 therefore omitted. It is to be also observed, that the 

 enumeration of generations as immediately successive, 

 as 1-2-3 etc., is to be understood as indicating succes- 

 sion only, and not any exact number of generations. 



In the hypothesis of heredity above outlined, it is 

 insisted that the effects of use and disuse are two-fold ; 

 viz.: the effect on the soma, and the effect on the 



