464 
DORIS L. MACKINXON. 
This stage^ with two large nuclei^ a large vacuole^ and 
clear alveolar cytoplasm, is iimcli the most abundant. I have 
looked in vain in iny small material for the fission of the 
cytoplasm whicli I believe follows, and for the escape of tlie 
two flagellates. Probably the cysts are passed out from 
the gut of the host in this binncleate state. 
In the second of my preparations, where there were no 
cysts seen, ten of the twelve small flagellates w’ere found with 
the karyosome eccentric, and possibly they had recently 
emerged from cysts (PI. 31, figs. 4-7 ; PI. 32, figs. 27-29). 
In these forms it was often impossible to trace the rhizostyle 
past the nucleus, into the anterior border of which it appeared 
to be inserted. (Cf. the flagellar apparatus in Oicomonas 
[see Hartmann and Chagas, 1910], to which this arrangement 
is very similar.) In one small individual (PI. 32, fig. 29) 
there were three nuclei, but I do not know what this 
indicates. 
In the cysts I have found no trace of fusion of 
the nuclei, nor any indication that there is a sexual 
process there. They seem to be simply multiplica- 
tion cysts. 
Systematic Position. 
As Alexeieff suggests (1911a), the affinities of Ehizo- 
mastix are probably on one side with free-living forms like 
Oicomonas and Cercomonas,^ and on the other with 
parasites like Herpetomonas and its allies. There is a 
striking resemblance between Oicomonas, as figured by 
Hartmann and Chagas;, and certain flagellate stages of 
^ I am unable to appreciate Alexeieff ‘s reasons (1911b) for removing 
Oicomonas from among the Cercomonadines. He speaks of its mode 
of eiicystment as resembling that of Monas. At present onr know- 
ledge of the eiicystment of Oicomonas and its allies is so scanty as to 
afford little i-elialile indication of their affinities, but I do agree that in 
the comparative study of such processes lies onr surest hope of 
ultimately bringing something like order out of the present chaos of 
flagellate classification. “Die Kenntniss der Entwicklnng ist 
das erste Postnlat der Protozoenf orschnng” (Schandinn). 
