Mutations and Evolution . 
219 
heredity and variation, have had a wide vogue in recent years. On 
the other hand, Loeb (1916) and from a different point of view, 
Ritter (1919), among others, have recently championed the 
organism-as-a-whole. The latter writer has pressed this view 
farthest, in the endeavour to eliminate elementalist conceptions 
altogether. We believe a truer attitude lies in the recognition of a 
fundamental truth in both these aspects. 
In a former work 1 and in earlier chapters of this series we 
developed a cell theory of mutations emphasizing the fact that each 
new form arises as a germinal difference from the parent type. The 
cell unit, in all such variations, is the thing which has changed, and 
the new external characters which appear in every part of the 
organism are the structural result of an ontogeny built up with 
a different unit as basis. 2 This situation was particularly clear in 
(Enothera gigas , where it was shown 3 that the volume of the nuclei 
and cells has increased in varying proportions in different tissues. 
Tupper and Bartlett (1916) have confirmed and extended these 
results in the case of CE. stenomcres mut. gigas which is also tetra- 
ploid or 4x in the constitution of its nuclei. 
Without going farther afield for confirmatory data, which are 
amply furnished in the contemporary literature, we may conclude 
that the mutation theory of germinal variations is firmly grounded 
upon the cell theory, and if the cell theory were universal in its 
application then mutations or germinal changes might be supposed 
to supply the whole of the material for evolution in organisms. 
Facts such as those pointed out above lead to the concept of the 
species cell. This is a conception which has been independently 
arrived at by different lines of approach (see, for example, Lang, 
1909). It is a sounder and less extreme conception than that of the 
organism as a cell-state, i.e ., merely an aggregation of more or less 
independent cell units. 
Biologists have long recognized the necessity for limitations of 
the cell theory of organic structure. On the one hand we have the 
legitimate and necessary conception of the species cell, briefly set 
' The Mutation Factor in Evolution. 
2 If this be the case, then the mitoses during ontogeny do not bring about 
the unequal division and sorting out of portions of the chromosomes, as 
Weismann supposed ; but all these divisions are, as they appear, equational 
so far as the chromosomes are concerned. This conclusion has also been 
reached from the study of experimental embryology (Conklin, 1916) and from 
other lines of approach. So far as the chromosomes are concerned, their 
materials are apparently not as a rule segregated by differential divisions 
during ontogeny. On the other hand, differential divisions of the cytoplasm 
are of frequent occurrence. 
3 Gates, 1909a. 
