io62 The American Naturalist. [December, 
represented as follows, for successive generations, which are num- 
bered, I, 2, 3, etc. 
Under the appropreate stimulus the soma acquires A and the 
germ plasma the identical a)- as the first stage. The character 
Ad)- being only inheritable via the germ-plasma, it is represented 
by c^ in the second stage or generation, where it appears as an 
addition to the characters of S and g, so that the soma of the 
second generation is represented by the expression Sa^, and the 
germ plasma by g {a}') ; (on the supposition that S A -\- ga^ re- 
presents 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 represented 
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 d' appears in the soma, which now becomes 
Sa^d^. The a'^ acquired by the germ-plasma of the second stage, 
is inherited by that of tlie third, which is therefore represented 
hy g{a^a~). To the third stage is now added the acquisition 
Ad\ The a^ is again incorporated into the soma of the suc- 
ceeding or former stage, which is therefore represented by the ex- 
pression SdWa^] while the germ-plasma of the same (fourth, 
"4,") stage, is represented by g{a^d^a% and so on. The lines 
of immediate 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 repre- 
sent the transmission of the same characters to the soma into 
which it grows, as the succeeding generation or stage. 
The letters rt\ a^, etc., expressive of characters acquired by the 
germ-plasma, are numbered for identification 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 enumer- 
ation of generations as immediately sucessive, as 1-2-3 etc., is to 
be understood as indicating succession 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 
