W. F. R. Weldon 
307 
The negative result so far obtained may conceivably be due to either of three 
causes : 
(1) The characters of the shell-spiral investigated may not be now subject to 
selective elimination in G. itala at all; the correlations already established between 
the various dimensions measured may result in such mutual adjustment of the 
parts that within the narrow limits of observed variability any combination of 
magnitudes of these dimensions, which actually occurs, is sensibly as efficient as 
any other. 
(2) The construction of a garden and of public walks round the Citadel of 
Brescia is a recent thing, and has possibly led to a recent introduction of Glansilia: 
the condition of the walls of the Citadel is certainly not at present that of an im- 
portant military fortification; the growth of herbage, the falling out of mortar, and 
other conditions favourable to the multiplication of Glausilia, have certainly been 
emphasised during the past few years. It is therefore jDOSsible that we have here 
a new colony, multiplying under exceptionally favourable conditions, and so exempt 
from forms of selection which affect the species in other localities. 
(3) The individuals measured, both young and old, were gathered in early 
spring, after their winter sleep. It is possible that selective elimination of the 
young takes place largely during the winter, and that individuals of the same 
length, collected in the autumn, at the close of their period of growth, might be 
more variable than those which survive the winter. 
The data at present available do not permit us to decide which of these 
suggested possibilities represents the truth. I hope to collect evidence on the 
point during the autumn of this year; I have ventured to publish this preliminary 
note because the failure to demonstrate selective elimination in any such case as 
this appears to me in itself a result of some importance. 
