N. CUNLIFFE 
207 
Finally such a mode of expressing the results allows the aberrant 
variant to be picked out at once. Two individuals only are strikingly 
abnormal in size, one measuring 3'3 x 2‘9 mm. and the other 
4'6 x 2’8 mm.; in each case, size only is abnormal, the other characters 
being similar to those of individuals of similar breadth. 
These differences in size may be due either to an intermingling of 
two or more species or varieties, which are difficult to separate, or to 
the variability of a single species. In the “ male ” frequency curve 
(Fig. 2, </) for which, unfortunately, less material was available than 
Fig. 2. Frequency curves, male and female. 
was to be desired, it will be noticed that the individuals tend to group 
themselves about the means, and that such a division is absent in the 
“female” curve (Fig. 2, $ ). If the division in the former curve were 
due to the intermingling of two species or varieties, it would probably 
show also in the latter; as it does not show here, it may be assumed 
that only one species is present and the explanation of the division in 
the “male” curve is to be found in the artificial selection mentioned above. 
The occurrence of a tendency to dimorphism in the male would explain 
this result equally well, but is not a necessary assumption. 
