BIONOMICAL INVESTIGATION OF THE NORFOLK BROADS. GG7 
recorded year by year. I believe that the recording of even a few 
groups will give us very interesting results, and we may possibly, 
apart from the bionomics, get some valuable information as to the 
influence of physical conditions upon local distribution. However, 
the first point to my mind is to get as many instances as possible 
of localised distribution within our district and then proceed from 
that knowledge to enquire into the causes of such distribution. 
I believe that if about ten of the stations — chosen so as to fairly 
represent the whole district — are worked thoroughly, they will give 
us most of the material we require. I do not suggest that the 
remaining fourteen sub-districts should bo studiously avoided, but 
it must be remembered that the non-discovery of a species is not 
such good evidence of its non-occurrence as its capture is of its 
presence, and that in consequence it will be necessary to take 
considerable trouble to get as reliable a list as possible in the ten 
primary sub-districts. Records of the occurrence of species in the 
intermediate secondary sub-districts will be useful as extending the 
distribution of these species, but the absence of such records need 
not be taken as showing the limits of the species. 
I propose to consider the following ten sub-districts as primary : 
Sutton, Catfield Fen, Ranworth, Wroxham, Burgh or Muck 
Fleet, Ormesby, Calthorpe, llickling, Horsey and Martham, regard- 
ing the remaining fourteen sub-districts as secondary. 
Now in order to convince you that there is such a phenomenon 
as local distribution in the selected district, 1 will refer to the 
small amount of work which has so far been done. Mr. Scourfield 
has from time to time, since 1890, visited the district for the 
purpose of collecting Entomostraca, and has kindly placed his list 
of captures at the disposal of the Laboratory. From his list and 
that of Mr. Robert Gurney, who has done most of his work, though 
not all, during the last year, I have tabulated the local distribution 
of the Cladocera and Copepoda so far as it affects our district — (the 
records of the Ostracods are not sufficiently complete to include) — 
and the results are very much in accordance with those obtained 
for insects in Illinois. I have further tabulated the results of last 
season’s work to which Mr. Scourfield contributed in September, 
and I find that for the ten primary sub-districts, thirty-one species 
were not taken in localities where they were previously found. Of 
these, seven were not found in Hickling, one in Horsey, three in 
Calthorpe, fourteen in Martham, one in Ormesby, one in Burgh, 
