MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA. 30I 
It will be noticed that with the exception of Agabus nebulosus 
and A. bipustulatus there is no break in the record of species. 
With regard to the former species, I think it probably should 
have occurred immature in August, and with regard to the 
three or four specimens of the latter producing the record in 
September, I was very uncertain at the time of finding as to 
whether they were really soft or not. Leaving out, however, 
these two possible exceptions the records suggest one hatching 
period only, lasting perhaps many weeks, but still one period. 
I am, therefore, now inclined to think that all the evidence 
with regard to egg-laying, larvre and immature imagos, 
although scanty, points to one cycle only in the year and not 
two, as I previously suggested. 
If this idea is correct we have still to account for the double 
hump curve of the Hydradephaga distribution which was so 
conveniently accounted for on the hypothesis of two hatching 
periods. I do not doubt that had I collected in the district 
in July of last season, I should have found a similar falling 
off in distribution to that which was so marked in 1904; but 
even without this evidence, the 1905 curve is truly double 
humped, the two maxima being in June and September just 
as they were in the complete curve for 1904. 
I have already mentioned that I was interested in the 
question as to what happens to the Water-beetles when their 
home pond or dyke dries up, and as this may have some bearing 
upon the nature of the distribution curve, I will recount my 
observations. In the first place the majority, if not all, the 
Water-beetles have efficient wings, and some species, especially 
of the genera Octhebius and Anaccena, readily take to flight on 
a bright hot day when they find themselves stranded upon the 
collecting sheet. Agabus bipustulatus, L., is occasionally to be 
seen flying about on hot days, and also in such weather is liable 
to use its wings when dropped upon the dry, hot ground. The 
natural conclusion to draw from their possession of usable 
wings is that, as soon as the home-pond or dyke dries up, 
the individuals will betake themselves to some other patch 
of water. There are, however, two facts which tend to show 
that the Beetles do not do this ; one is that in the driest season 
x 2 
