66 MR. F. BALFOUR BROWNE ON AQUATIC COLEOPTERA 
worms, and such forms, whereas the Palpicornia, although 
animal feeders in their larval condition, are vegetable feeders 
in their perfect state. 
Now the various forms of lower animal life in the water 
are abundant all through the summer and autumn, but die 
off very rapidly about the end of October. They are more 
or less scarce through the winter, but the numbers begin to 
increase again when the temperature becomes suitable in 
the spring. The Hydradephaga, therefore, can find food 
almost everywhere during the summer and autumn, so that 
the tendency of the individuals to wander receives no check. 
The species which hatch in the early part of the year spread 
over the district, and the maximum of species in the imago 
state in September is not due to the appearance of new 
species so largely as to the hatching out of a second generation, 
for very few of the species recorded in September have not 
been recorded in other months also. 
If then, as I believe, the distribution curve for 1904 shows 
what takes place annually, why is the distribution of species 
in spring so poor after the promising autumn distribution ? 
The only suggestion I can make is that winter conditions 
directly or indirectly kill off imagos and larvae of the various 
species in those stations to which they have spread during 
the summer, so that each spring the process of distribution 
begins again from the comparatively small number of stations 
at which the larvae, or in some cases the imagos, have 
survived. 
Now plants, upon which the imagos of the Palpicornia 
depend for their food, carry out all their development in the 
spring and early summer, and by August and September, 
flowering being past, they are no longer succulent and sweet, 
and the leaves and stems have become coated with minute 
organisms, giving them a muddy appearance. 
The spring hatch of the imagos of the Palpicornia, which 
takes place in April and May, sees the commencement of 
the process of distribution. Food is plentiful, and the 
insects can find fresh green leaves in most of the dykes and 
ditches. After July, however, the food in many places 
