PREFACE. 
THE main object in the preparation of this work 
was to bring together, as concisely and accurately 
as possible, in a single manual, all that has been 
so far discovered regarding the British Freshwater 
Rhizopoda and their near allies the Heliozoa. The 
labours of Dr. Penard of Geneva have resulted in 
his giving to the world exceedingly valuable mono- 
graphs of the Rhizopoda and Heliozoa of Central 
Europe, and of Switzerland in particular; and it 
is to be regretted that no British Biologist of 
equal standing has done the same for this country, 
which is certainly not less rich in species. 
The present attempt at a classified description 
of these microscopic animals will it is hoped lead 
to other workers entering upon a field of research 
which is fascinating in a high degree even to the 
general microscopist. The biological student will 
find in this manual an honest effort, at least, to 
describe the species which have hitherto been met 
with in this country, to give their usual habitats, 
and to point out the characters by which they may 
be most easily identified. 
I do not profess to have investigated very close- 
ly the physiological problems associated with the 
life-histories of these organisms; the minute and 
continuous observations which are necessary for that 
