29O MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA. 
X. 
A STUDY OF THE AQUATIC COLEOPTERA 
AND THEIR SURROUNDINGS IN THE NORFOLK 
BROADS DISTRICT. 
(Second Paper.) 
By Frank Balfour Browne, M.A. (Oxon.), F.R.S.E., F.Z.S., 
Director of the Sutton Broad Laboratory. 
Read 2 jth February, 1906. 
In my previous paper upon the Aquatic Coleoptera and their 
surroundings in the Norfolk Broads District, I referred to 
some of the facts which I had observed during the season 
1904 as to the occurrence, distribution and habits of this 
interesting group. I worked out the number of species per 
collection per month, and drew curves giving a graphic 
representation of the results, and from the curves thus obtained 
as well as from the fact that crowded centres of various 
species occurred especially in spring and autumn I suggested 
that there were probably two seasons of the year in which 
imagos hatch out from the pupal condition, that at least 
many of the species have two broods in the year, and I con- 
sidered that the crowded centres were centres of distribution 
of the various species. 
With another season’s experience in the collection of these 
interesting water insects, I come here with the intention of 
correcting and modifying some of the explanations of facts 
which I gave last year. The necessity for correction depends 
partly upon the fact that I have discovered that a method 
upon which I based my record of species per collection per 
month, in mapping out the curves for my last paper, is quite 
unsuited to the purpose under the circumstances. 
