STRUCTURE AND LIFE-HISTORY OF COPROMONAS SUBTILIS. 83 
apparatus. On account of the small size of the animal it is 
exceedingly difficult to be quite certain of the exact inter- 
relations of these parts. At times the basal granule seems to 
be situated on the posterior part of the reservoir, from which 
the flagellum then arises. This arrangement somewhat 
resembles that seen in Euglena, as described by Wager (52), 
but in Copromonas no forking of the flagellar insertion can 
be seen. When such a condition exists the flagellum appears 
to cross the reservoir, thus lying for a short distance within 
this structure. 
The nucleus (N.) lies somewhat posteriorly, and is not con- 
nected in any way with the flagellum, as is so often the case 
in flagellates (cf. Plenge [82], etc.). In the living monad it 
appears as a greyish, spherical vesicle, shghtly more refractive 
than the surrounding cytoplasm. In stained preparations, 
however, it can be seen to possess the structure shown in the 
diagram. That is to say, it consists of a central, deeply- 
staining chromatic mass, surrounded by a clear zone which 
contains practically no chromatin. Surrounding this is an 
achromatic nuclear membrane. Achromatic strands unite the 
membrane with the central portion. I have found that the 
structure of the nucleus is most easily demonstrated as 
follows: A small drop of solution containing the monads is 
placed on a glass slide. A small drop of a solution of methyl 
ereen in | per cent. acetic acid is then placed in the centre of 
a coverslip, which is carefully lowered on to the first drop. 
The coverslip is then pressed firmly down, and the prepara- 
tion examined withthe waterimmersion. In such a preparation 
the central chromatic part of the nucleus is coloured green : 
the nuclear membrane swells out slightly and becomes very 
distinct. Many other details of the anatomy can be made out 
in this way. 
It will be seen that the nucleus is of the second type dis- 
tinguished by Prowazek (36) in Flagellata (see infra, p. 104). 
The posterior region of the body is usually more or less 
filled with food masses. These are of varying sizes, and 
formed in the manner described below (p. 86). Outside the 
