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H. M. WOODCOCK AND O. LA PAGE. 
from the general protoplasm. We may say here that there 
is not the faintest hint of any groove or depression around 
the body of a crescent at the point where the flagellnm starts. 
Not the least remarkable feature of Selenomastix is its 
cytology. The best stain is undoubtedly iron-hgematoxylin. 
DelafiehTs hgernatoxylin shows just the same minute structure, 
but it has the drawback that the flagellum is usually very 
faintly stained and often cannot be made out, and the same 
remark applies to carmine stains. Giemsa^s stain is of con- 
siderable use in many respects, but not of much service in 
bringing out the details of the internal structure of the body, 
except where the chromatin is in the form of one or two 
prominent masses. The general protoplasm nearly always 
stains uniformly and homogeneously, sometimes lighter and 
sometimes darker, according to the degree of extraction. It 
never shows either granules of any kind or vacuoles. 
There is no properly constituted nucleus, either of the 
usual karyosomatic type seen in the flagellates, or of any 
other type with which we are acquainted. Nevertheless, 
chromatin is undoubtedly present in greater or less quantity, 
occupying a peculiar but characteristic position. The prin- 
cipal situation of the chromatinic substance is at the periphery 
of the body. In the condition in which the parasite has 
apparently the least amount of chromatin, this constitutes a 
very narrow layer or zone, extending all over the surface of 
the body and appearing in optical section as a definite border, 
staining blacker and more intensely than the cytoplasm 
(figs. 3, 5, 6). More generally, however, this layer shows 
distinct thickenings, which may take the form either of 
numerous fine, small grannies, appearing as little more than 
dots (figs. 1, 4, 8) ; or of few or several larger more con- 
spicuous grains or small masses (figs. 9, 11, 10, 17) ; or, finally, 
of a few (usually one or two) quite large, dark-staining masses 
(figs. 12-16, 26). The granules and masses project inwards, 
one edge always being at the surface of the body, and we are 
inclined to consider them as having developed from the basal, 
peripheral zone or layer. Now and again these dark masses 
