The Theory of Evolution 223 
ous or regularly broken, and these latter by fusing produce even 
cross-bands. A band may be absent or two bands may unite 
into one, etc. It is possible, as has been said, to arrange these 
variations so that a continuous series is formed. Lang con- 
cludes for these snails that “‘there exist colonies in which two 
forms are found that behave like well-defined mutations, but 
which are connected in other colonies by continuous series of 
intermediate forms that appear to be variations.” Lang has 
begun an experimental examination as to whether these “varia- 
tions”? are themselves constant, 7.e. whether true races exist 
within the population, or whether there is simply a continuous 
fluctuation between the extremes of the series. He has already 
determined that a large number of these varietal characters are 
inherited to a high degree. Many forms of banding exist, such 
AS 12345, 10305, 00300, 00345, 00045, with the colors white, green- 
ish yellow, orange-yellow, red; also the intensity of the coloring, 
the opacity, and the dotted condition of the bands. Even 
the breadth of the bands and different forms of fusion of the 
oo Re 
bands, such as 12345, 12345, 12 345, are inherited. Lang states 
his conviction that further research will reveal that there is 
scarcely a single, or at least very few characters that may not 
be hereditary. In such cases it is possible to separate the pure 
lines from a complex population. Lang also states “that almost 
every character may appear at one time with the heritable char- 
acter of a mutation, and at another time with the not heritable 
character of a fluctuating variation.” The difference between 
a mutation and a variation must rest not on the criterion of dis- 
continuity or of saltation on which “‘so much stress has been 
laid, but on the character of the heredity.” Fluctuating varia- 
tions differ quantitatively, mutations qualitatively; but Lang 
thinks it advisable not to draw too sharp a line between the quan- 
titative and qualitative differences. 
These studies of Lang recall the observations of Gulick on 
the land snails of the Sandwich Islands, where almost each valley 
has its peculiar variety. There seems to be in this case a highly 
mutable species. Experiment alone can fully settle this point. 
