OXNERELLA M A K IT IMA. 
523 
differentiated in the centre of this minute darkly-staining 
mass (PL 27, fig. 4) ; and still other specimens show gradual 
transitions to the “ typical ” form of centroplast (PL 27, 
fig. 5). Further, organisms can also be found in which the 
whole centroplast seems to have greatly increased in size 
(PL 27, fig. 6). The central granule is larger, and the clear 
zone separating it from the membrane has also expanded. 
In such specimens the axial fibres seem no longer to termi- 
nate on the membrane, but to pass through it to the central 
granule. I believe they are actually attached to this, but 
from the very small size of all the structures it is hardly 
possible to be absolutely certain of their relations. This last 
condition (PL 27, fig. 6) affords an easy transition to that 
first described (PL 27, fig. 3). 
The appearances just described strongly suggest that 
cyclical changes occur in the centroplast of the “ resting ” 
animal. Similar appearances have already been described 
and thus interpreted in Wagnerella (Ziilzer, 1909). Com- 
parison, moreover, with the cyclical changes described in the 
centrosome of the metazoan egg (Vejdovsky and Mrazek, 
1903) at once suggests itself. Although both the interpreta- 
tion and the comparison appear to me justifiable, I am not 
completely convinced of their correctness ; and I am at a 
loss to understand what function the “ cyclical changes ” in 
Oxnerella can subserve. I thought at one time that they 
might perhaps play some part preparatory to the division of 
the organism — for the centroplast has, as will be seen later T 
an important function in this process. But since the structure 
of the centroplast is “ typical” (PL 27, fig. 5) immediately 
before division and immediately after, this seems to me im- 
probable. There is no obvious reason why it should pass 
through a cycle of changes — returning finally to its original 
condition — during the interdivision period. 
General Account of the Process of Division. — 
Before describing in detail the successive phases of division 
it will be convenient to give a brief general outline of the 
process. 
