140 FAUNA AND FLORA OF NORFOLK : ROTIFERA. 
once, as many Rotifers die quickly when the air is 
excluded. 
When the search is to begin, it pays to have a strong light 
and to set the bottles and tubes close to it, as Rotifers often 
swim towards the light, and can be more easily taken with 
the pipette from the bottle and transferred to the microscope 
tank. 
Having secured good illumination with a dark background 
and filled the tank by drawing the water from bottle No. 1 
with] a big pipette, we put in a bit of weed and the search 
commences, and a list is made for that locality. 
Three or four fillings of the tank will generally exhaust 
most of the Rotifers from even a large bottle , and my tubes 
generally hold about two tanks full. 
In my system of recording 1 always endeavour to give some 
idea of the abundance or otherwise of a species, and it is strange 
in a place like Sutton Broad how much this varies in different 
parts of the Broad. For example, in the Heater, 55 species, 
in the main dyke close by, 30 species were found. 
I 12 in M.D. not in Heater 
Total 67 - 18 in both. 
I 37 in Heater not in M.D. 
Out of the 18 found in both 
10 were more common in Heater than in M.D. 
6 were about equally common, or rare. 
2 were more common in Main Dyke than in H. 
That is only one example of the erratic occurrence of species. 
It seems to me that the occurrence or the frequency of 
occurrence of a species is quite a matter of chance within even 
a few yards of the same piece of water, and under the same 
conditions of wind, depth, vegetation, bottom, etc. Certain 
spots are, however, always good, and one can tell almost at 
once which is likely to be good by the vegetation. I gave a 
thorough trial to Sutton Broad, and took a fair sample of 
Barton, but the wind checked me in the latter case, except 
on Thursday, 10th. 
My programme was as follows : 
Monday, 7th. Sutton Broad Heater and Dykes on the way 
there, and on towards Stalham. 
