044 I' chicles of the Hereditary Characters. 
this kernel is a sufficient basis for experimental investi- 
gation, and that it is far more likely to lead to the dis- 
o - 
covery of new important facts than the elaborate tissue 
of hypotheses which have grown up around it. More- 
over pangenesis is capable of much closer application than 
the opposite view that each of the units bears the whole 
of the specific characters. I confidently recommend DAR- 
WIN'S principle to any one in search of new lines of re- 
search in this field. 
In the first place it has led to the proper distinction 
between the two main types of variability, viz., muta- 
bility and variability in the restricted sense. ''Finally, 
we see," says DARWIN, "that on the hypothesis of pan- 
genesis variability depends on at least two distinct groups 
of causes." The first group embraces the failure, the 
over-production and the change in position of particles 
without their being themselves transformed in the pro- 
cess. These changes can explain a great deal of fluctu- 
ating variability. Into the other group fall the changes 
in the particles themselves producing new types which 
in multiplying will develop into new characters. 
Into these categories fall three main types of varia- 
bility, since the first group is obviously a twofold one, 
embracing in terms of my present view, on the one hand 
fluctuating variability, and on the other the regressive 
o 
and degressive mutations. The former may be caused by 
changes in the number of the pangenes ; the two latter, 
however, by the "transposition of gemmules and the re- 
development of those which have long been dormant." 
Besides these the origin of new forms of pangenes ob- 
viously corresponds to progressive mutability. 2 
1 Animals and Plants under Domestication, II, 2d ed., 1875, P- 39O. 
2 See also Intracclhtlar Pangenesis (Engl. ed.), pp. 73 and 214 
