58 MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA 
I believe that further experiments will show a direct 
connection of the sexual cycle with the season, determined 
probably by the average temperature, and that the sexual 
individuals of the second (autumn) cycle are not wholly, or 
even largely, derived from the resting eggs of the previous 
cycle, but are their descendants by agamic reproduction. 
There is one more question to discuss. Which is the 
original method of reproduction, sexual or asexual ? I cannot 
go at length into this question, and will only say that the 
evidence is strong that originally sexual reproduction with 
resting eggs was the rule. That parthenogenetic reproduction 
arose and prevailed from the advantage conferred by reason 
of the greater rapidity of multiplication made possible by it. 
By multiplying individuals before the production of resting 
eggs set in the species was more assured of persistence. 
In some cases agamy has supplanted amphigony, but 
generally it has been necessary to preserve the faculty of 
producing winter eggs. The conditions which we see now 
in regard to cyclic reproduction of each species and in each 
country are to be regarded as adaptations to the necessities 
of the situation and of the species. 
VI. 
A STUDY OF THE AQUATIC COLEOPTERA AND 
THEIR SURROUNDINGS 
IN THE NORFOLK BROADS DISTRICT. 
By Frank Balfour Browne, M.A., F.R.S.E., F.Z.S., 
Director of the Sutton Broad Laboratory. 
Read February 2 8th, 1905. 
A year ago I read a paper before this Society in which 
I attempted to lay down a scheme of work for the investi- 
gation of bionomical problems in our district. The scheme 
