96 THE VARIATION OF ANIMALS IN NATURE 



is far more marked in nemoralis. The ' spread ' 

 of variation is more limited ; actually two 

 out of the four colour-classes only are repre- 

 sented, though a few ' brown ' occur at three 

 colonies. In one colony (Maiden Castle) 

 one class is 77 % of the population. In banding 

 the spread was fairly wide, though usually 

 one or two classes tend to be more highly 

 represented. 



(d) Rensch (1932) calculated the percentage frequency 



in 16 colonies of Cepea nemoralis (mostly remote from 

 each other) for 7 colour- and band-classes. The 

 statistical significances of the differences were not 

 worked out. From his table we may give the following 

 results on ' spread.' In four colonies one class was 

 found in over 90 % of the specimens ; in four, one 

 class was over 70 % , and in one a class was over 

 80%. In the rest the tendency was for two classes 

 to be well represented and the others to be numerically 

 inferior. Very often three or four classes are entirely 

 absent. Two classes, yellow 00000 and yellow 12345, 

 have a very high frequency and are about equal in 

 frequency, and the others are all very low. 



(e) Crampton's work (1916, 1925 and 1932) is on a 



much larger scale than the rest. It is, in fact, so 

 extensive and the details are so manifold that one 

 awaits a summary and analysis by the author and 

 only the following points can be noted here : 



(i) The spread of variation tends to follow the same 

 lines as in (d), i.e. there is a tendency for one 

 or more classes to be preponderatingly frequent 

 and some colonies may lack a whole series of 

 classes, 

 (ii) Adjacent colonies tend to be alike, but the same 

 percentage of a given class may be found in 

 remote colonies. Abrupt change in the number 

 of classes and their percentage frequency is 

 found between adjacent loci, and the latter 

 may differ in the absence and presence of 

 whole classes. 



