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CLIFFORD DOBELL. 
found it impossible to study the dividing nucleus in unstained 
specimens, on account, probably, of the small size of all the 
structures concerned. Elongated organisms- — which are seen, 
in stained specimens, to be at any stages of the prophases or 
metaphase — complete their division in times varying from 
about five minutes to a quarter of an hour. These are the 
only living forms which I have been able to recognise as 
forms about to divide; and they are actually, as will be 
evident, already somewhat far advanced in the process. On 
analogy with other organisms, and from the few observations 
which I have been able to make, I should estimate the total 
time taken for division at about twenty minutes to half an 
hour. 
5. Some Remarks on the Centroplast of the Heliozoa. 
I propose to terminate this account of Oxnerella with a 
brief consideration of certain problems presented by the 
centroplast. Although this organ is probably peculiar to a 
small section of the Heliozoa — for it is not known to be 
present in any other organisms — a consideration of its 
functions and homologies leads to some of the fundamental 
problems in the morphology of the Protozoa. 
The facts so far established concerning the centroplast may 
first be enumerated before their interpretation is discussed. 
They can, I think, be best reviewed in their historic order. 
The centroplast appears to have been first seen in Acan- 
thocystis by Grenacher (1869). He figured it, and described 
it as “ a tiny pale corpuscle ” lying at the centre of the 
organism. He believed, moreover, that the axial fibres of the 
pseudopodia were rooted to it; but he was unable, as he says, 
4t to prove a direct connexion.” The proof was, however, 
soon furnished by F. E. Schulze (1874), R. Hertwig (1877), 
and others. All later workers have confirmed their observa- 
tions, and extended them to all the Heliozoa known to possess 
■centroplasts. 
The anatomical relations of the centroplast having been 
