STRUCTURE AND LIFE-HISTORY OF COPROMONAS SUBTILIS. 103 
the cytoplasm. Large clear vacuoles appear at any point in 
the creature’s body, and the reservoir often reaches enormous 
dimensions—sometimes completely filling the anterior half of 
the animal. 
The nucleus increases in size at first, but later breaks up 
into small fragments of various sizes. The cytopharynx 
appears to dissolve. As the animal dies it comes to rest, and 
the flagellum ceases to move. If it be watched at this stage 
it is seen to gradually fade away—apparently dissolving. 
The dead monad is permeable to bacteria at only one spot— 
the cytostome. Through this bacterial invasion comes, First, 
the minute bacilli enter, but later, as the breach is widened, 
hordes of large bacilli and spirilla force an entry. At this 
stage the corpse is a mere bag containing a seething mass 
of microbes. As the nutritive remains of the monad get 
exhausted the bacteria gradually forsake their prey, until 
finally nothing but the skeleton of the monad—consisting of 
the cuticle—is left. The cuticle is thick and very resistant. 
It persists for a very long time in the form of an open sack, 
the opening marking the site of the former cell-mouth. 
It is worthy of note that one can often observe degenerat- 
ing monads side by:side in the same drop of fluid with per- 
fectly healthy individuals in active division or conjugation. 
The bacteria are usually most dense during the second day 
and thereabouts, but degenerating monads are not usually 
seen until several days later, when the number of bacteria 
has very greatly decreased. 
GENERAL DIscussIon. 
(1) Nucleus, Flagellum, and Basal Granule. 
I propose to say in the following pages a few words about 
some of the more interesting points which a study of the 
morphology and life-cycle of Copromonas raises. In the 
first place, I must say something about the morphology of 
