522 
CLIFFORD DOBELL. 
“ central granule” is a periphrasis which does not 
correctly describe its structure, nor indicate its most important 
functions ; and for brevity, and also for other reasons which 
will be clear later, I propose to call the organ in question a 
centroplast. 
In a living Oxnerella the centroplast is with some diffi- 
culty visible as a minute spherical corpuscle lying at the 
centre of the organism (PL 27, fig. 1). It is rather feebly 
refringent, and is surrounded by a clear zone of protoplasm 
quite free from all food-bodies or granules. The size of this 
zone varies a good deal in different individuals. Radiating 
from the centroplast and traversing the clear zone in all 
directions can be seen the central ends of the axial fibres of 
the pseudopodia. 
In fixed and stained specimens all these structures can be 
studied in greater detail. The centroplast itself (PI. 27, 
figs. 2, 5) generally appears as a minute clear sphere with a 
deeply-staining granule at its centre. The periphery of the 
sphere stains deeply, as though it were clothed with a very 
delicate membrane. The axial fibres, when traced through 
the clear zone of protoplasm towards the centroplast, appear 
to terminate in minute knobs or granules on its external 
membrane, and cannot as a rule be traced beyond this to its 
central granule (PI. 27, fig. 5). 
The central granule of the centroplast stains deeply with 
iron-liaematein, less deeply with carmine stains. In its 
entirety the centroplast thus resembles a tiny nucleus with a 
karyosome and nuclear membrane. 
If one examines with care the centroplasts of a number of 
different individuals, it can be seen that they do not all pre- 
sent the appearances just described, though these are the 
most usual. In certain individuals no differentiation into 
central granule and surrounding membrane can be discovered. 
The entire centroplast is a minute, deeply-staining, and 
homogeneous dot (PI. 27, fig. 3), to which the pseudopodial 
fibres appear to be attached directly. In other specimens 
a very minute central granule appears to have become- 
