306 MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA. 
that unless the earth remains sufficiently moist the pupse will 
perish in the ground. If this explanation is the correct one, 
there is some evidence that the Palpicornia tend rather to 
inhabit waters less liable to dry up as their August distribution 
appears to be normal. Possibly, however, the excessive falling 
off in September of species per collection of this group may be 
accounted for by the fact that some of their pupae had been 
reached by the excessive dryness. 
The October portion of the curves of both the Hydradephaga 
and Palpicornia is, I think, to be accounted for partly by the 
fact that the marshes were then flooded, so that the individuals 
tended to become more distributed instead of being collected 
into the dykes, and partly by the fact that the mean temper- 
ature of the month was several degrees lower than that of 
October, 1904, which would tend to kill off some individuals 
earlier and cause others to hibernate earlier than they would 
otherwise have done. 
I have in the. present paper confined myself to a discussion 
upon the curves of species per collection per month, which 
I believe are now worked out upon a sound principle. I have 
endeavoured to correct some of the conclusions which I came 
to in my previous paper and have substituted others which, 
from additional observations, appear to suit the case more 
satisfactorily ; but I am quite prepared for the possibility 
that after another season my present conclusions may again 
require re-forming. Almost nothing is known as to the habits 
of this group and I might almost say of any group of insects, 
and the manner in which physical and meteorological con- 
ditions affect these forms of life has so far scarcely received 
any consideration. 
Entomology is still chiefly a playground for the collector, 
who sees nothing in an insect except an addition to his cabinet. 
Such an individual is of necessity a systematist since he names, 
not always correctly, the species which he captures and 
sends his doubtful lists to the entomological journals; he is 
often a man with little or no training or qualification for the 
work, but if he advertises himself sufficiently in the entomo- 
logical papers he receives specimens for identification from 
