70 SECTIONAL ADDRESSES 
species,’ 19 a term which does not commit one to an interpretation of the 
phenomenon. I have been studying one of these complexes for some 
years and it consists of a series, at one end of which is what Fabricius 
named (Deronectes) depressus, while at the other end is what Panzer named 
(Deronectes) elegans. Both extremes undoubtedly have as distinct specific 
characters as any of the previously mentioned pairs. The general shape 
differs ; although the type of marking and colouring is the same in both, 
elegans is distinctly brighter than depressus. ‘The anterior claws of the 
male depressus are large, somewhat straight and sharply hooked towards 
the apex, while in elegans male they are more delicate and more evenly 
curved from base to apex. Further, the zdeagus is broad with a bluntly 
rounded apex in depressus and narrow and tapering to a point in elegans. 
But between the two extremes of each of these characters there are 
intermediate stages and one can form a complete series from one end to 
the other. A distribution map, based upon the width of the aedeagus, 
making six intermediate stages, shows that depressus is more northern and 
western and elegans more southern and eastern, and depressus is definitely 
more a peat form than elegans. The question arises: Is this a variable 
species controlled by climatic or edaphic conditions ? Is it two biological 
races in process of formation or are these two species which interbreed ? 
At the present time I am trying to solve this problem in the only way I 
can think of, by keeping depressus in my aquaria in Somerset under 
conditions in which previously elegans has lived and bred, and I am 
wondering whether, in the course of several generations, I shall find that 
they have become elegans. 
Now it must be admitted that, although my studies of these water- 
beetles have led me towards the view that new species may arise by the 
means I have suggested, proof is still lacking and the view that acquired 
characters are inherited is still a pious hope rather than a proved fact. 
But in connection with the gap in the evidence on this subject, in the 
case of the water-beetle clusters referred to, it must be pointed out that 
we have no evidence that the species-characters distinguishing the pairs 
are really heritable and not merely the effect of the environment upon 
each succeeding generation. There is evidence from other groups of 
animals that acquired characters may not disappear directly after the 
stimulus which caused them has been removed. ‘Therefore, it may well 
be that, in these water-beetles it would take a number of generations 
before any change would appear in the characters by which they are 
‘recognised. But, besides the possibility of these species having arisen 
in this way, there is another, based upon the work on Drosophila and 
Oenothera, where it has been shown that new characters may arise from 
changes in the chromosomes of the germ-cells, so that we can still ask 
the question, did the ancestors of water-beetles go into the water by 
choice and then develop adaptive characters, or did changes in form and 
structure create the choice by reason of which these beetles took to an 
aquatic life ? 
19 “The Aquatic Coleoptera of the Scilly Islands, with some remarks upon the 
Genus Philhydrus and upon “‘ Composite Species,” ’ £.M.M., vol. 68, 1932. 
