The Puny cues. 649 
of the hybrid to live, and in the second place the fertility 
of the hybrid itself. If, however, they are fertile, the 
unpaired characters probably simply divide in the primary 
hybrids, at the moment of sexual reproduction, in a vege- 
tative way, and this would explain the constancy of such 
hybrid races. 
Progressive mutations are due to the formation of 
new pangenes. Dissimilar entities arise in the idioplasm 
instead of only similar ones, and this is the process 
which we have called pre-mutation. The pre-mutated 
pangenes tend to be inactive at first, either because they 
do not exist in sufficient numbers or for other reasons. 
Obviously it is very probable that in different species 
similar pangenes may lead to the origin of the same new 
pangenes ; and this might perhaps explain many phenom- 
ena of parallel progressive mutability. 
Lastly we must suppose that the pangenes, or groups 
of them in each of the conditions referred to, may be 
more closely or more loosely associated with the remain- 
ing ones. If the association is a close one it will remain 
the same through all generations, and the species or 
variety is immutable with regard to the character in 
question. If the equilibrium is an unstable one, the 
character in question is mutable ; and slight external in- 
fluences may turn it into a stable condition and thus in- 
duce the visible mutations such as those of the Oenothcras. 
Unfortunately, however, the nature of these influences 
is still unknown. The stable condition, which in this way 
arises out of the mutable one, can be either active or 
latent. 
It would be easy to extend this discussion further ; 
suffice it, however, to say that the relation of pangen- 
esis to new discoveries is everywhere more or less ob- 
