'60 MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA 
at many of the same places in successive months. By this 
means I was enabled month by month to compare the faunas 
in a number of the collecting places. The total number of 
collections made during the ten months was 1079 ; but in 
working up the material the February collections have in 
most cases been omitted as they were very few in number, 
and in some of the calculations the November collections 
have also been omitted, chiefly because many of the species 
had then disappeared from the collecting places. 
I will here explain what I mean by a collection : A collection 
consists of an indefinite number of sweeps of the water-net 
in a pool or pond or length of dyke until no more species 
appear to be present. The collecting-place may be as much 
as thirty yards of a dyke or ditch, or as little as five yards ; 
it may be a pond ten yards across, or a pool two feet square. 
In the larger places it may take from half an hour to an hour 
before the number of species seems to be exhausted ; in the 
smaller places a quarter of an hour may suffice, though very 
often the smaller places are more richly stocked than the 
larger ones, if not in species at least in individuals. 
At the commencement of the work it was necessary for 
me to take home whole collections of 100, 200, or even more 
individuals in order to identify the species, as many of 
them I had never seen before, and from want of practice 
it was often difficult to be certain as to the identification of 
some of the commoner kinds. As time went on, however, 
I came to know most of the species at a glance, and gradually 
the number of individuals which required special scrutiny 
became fewer, and I was consequently enabled to make more 
collections during the day. Complete lists of every collection 
were made as to species, but not as a rule as to number of 
individuals. This latter was done in most cases at the 
commencement of the work, but only in special cases later 
on when some particular importance appeared to attach 
to it. 
Now this systematic method of collecting has, I believe, 
not been carried out before. As a rule, those who make 
■collections of insects are either systematists or morphologists, 
