394. ALDO CASTELLANI AND ARTHUR WILLEY. 
the monozoite has escaped. In such cases the orifice of exit 
can still be discerned. 
In some cases at the moment of fixation of the blood-film 
on the slide the monozoite had extended its body as far as 
the level of the nucleus, which appears constricted in the 
narrow orifice as if it were being squeezed through. Some- 
times only the hinder end remains within the cytocyst and 
corpuscle, the rest of the body being free. 
Occasionally, instead of emerging from the corpuscle the 
monozoite issues from its mother-cell again into the sub- 
stance of the corpuscle. This is probably a miscarriage. 
Sometimes the cytocyst is difficult to distinguish, and the 
monozoite appears to lie in the corpuscle without a sheath. 
In such cases the membrane can often be identified on close 
inspection, but not always. 
The monozoites which emerge from the cytocysts are all of 
one kind and of one size within the limits of a slight variation. 
Among the free-living forms in the plasma of the blood 
some are found to be about twice as bulky as others, indicat- 
ing that they continue to grow after becoming free. The stain- 
ing reactions of all are the same, namely, pale-blue cytoplasm 
and dense reddish-blue nucleus. 
We have been fortunate enough to find stages in the for- 
mation of the monozoite within the cytocyst, the substance 
of the former being only partly differentiated and merging 
imperceptibly into the protoplasm of its mother-cell, the cyto- 
cyst. Such differentiation as has taken place is indicated by 
the pale-blue staining reaction, but chiefly by the structure 
of the nucleus, in which the chromatin loops or threads are 
clearly visible, showing unmistakable signs of formative 
activity. 
With regard to the red-staining granules which we have 
mentioned above in association with the membrane of the 
cytocyst, we have interpreted these as belonging to a thin 
layer of residual protoplasm which is left round the periphery 
of the mother-cell after the formation of the axial monozoite. 
The membrane which is left empty within the corpuscle after 
