(ENOTHERA LATA AND (E. .MET. SEMILATA. 
559 
are not only of great value for clarifying our conceptions^ bnt 
they are necessary for accuracy in discussion and for obtain- 
ing a picture of tlie relationships between the various types 
of change. It is with these ideas in mind that the present 
classification of such processes is offered^ since these terms 
have been and are being used iu many senses by various 
authors. 
It has been urged that the term mutation ” should be 
used only iu the palaeontographical sense employed by 
Waagen^ but such limitatiou of the term seems undesirable 
for a number of reasons. In the first place Waagen was not 
the first to make use of the term, but it was emplo}^ed by 
botanists in a sense more nearly approaching its present 
usage long before Waagen^s time. Fm-ther, no law of 
priority with regard to such terms exists, and it is undesirable 
that any such law should be established. Moreover, the 
application of such a law would be impossible, for the signifi- 
cance of terms of this kind is of necessity constantly under- 
going modification with the increase in our knowledge of the 
phenomena of heredity and variation. In the few cases where 
there is a possibility of confusion arising, any difficulty may 
be overcome by defining one’s terms or by employing a more 
specific phraseology. Thus it would be easy to speak of the 
mutations of Waagen ” in contrast to the mutations of 
de Vries.” 
In the present state of our knowledge it seems desirable to 
define a mutation as a discontinuous germinal change arising 
from a physical or chemical alteration in the structure of the 
organism (in micro-organisms) or of one or both of the germ- 
cells (in higher organisms) which produce a new individual, 
or from such a change arising in certain cells elsewhere in 
the life-cycle of the organism, this change being capable of 
complete inheritance, at least in some of the offspring, though 
reversion may occur in the others. 
In short, a mutation is a germinal change which is com- 
pletely inherited in a portion at least of the offspring, though 
the others may show I’eversion. 
