STRUCTURE AND LIFE-HISTORY OF COPROMONAS SUBTILIS. 77 
investigation, I took the opportunity of working out the 
details of its life-history as far as I was able to do so. The 
present paper is the outcome of this, and although my work 
is incomplete it contains some observations which are of 
sufficient interest, I believe, for publication. I hope to be 
able at a future date to decide several points which at present 
remain obscure. 
In the later part of my paper I have given a very brief 
outline of some of the more important work which has been 
done on flagellate morphology and life-history. My reason 
for doing so is that it is impossible to discuss many of the 
problems connected with the flagellates without reference to 
recent work in this direction. And many important papers 
are in journals which are not readily accessible to the 
zoologist, and but few are in the Hnglish language. I am 
fully aware of the many omissions made from the literature 
of the subject, but my aim has been to contribute something 
towards our knowledge of the Flagellata, not to write a 
monograph on them. 
MatvEeRIAL AND MeruHops. 
Whilst I was working with the small parasitic Protozoa, 
which live inthe gut of our common frog (Rana temporaria 
L.), and toad (Bufo vulgaris L.), I often found it necessary 
to keep the contents of the alimentary canal for several days, 
in order to follow the development of the contained animals. 
A few days after removal from the frog the feces nearly 
always contained a small uniflagellate monad in great abund- 
ance. It is this monad whose life-history I am about to 
describe in this paper. 
In order to obtain a suitable number of the monads for 
investigation I find it best to proceed as follows: A frog or 
toad is killed and its large intestine removed. The contents 
are then carefully expressed into a small, perfectly clean 
glass dish and covered over with a glass plate. As the fecal 
matter thus obtained is usually too thick for microscopical 
