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 hke 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, i.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 foi-ms 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 



bands, such as 12345, 12345, 12345, 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 quahtatively; 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. 



