90 MAynArD M. METcALF, 
more diffuse granular or netted condition of chromatin enables it 
better to perform its chemical functions? We know from Meves’ 
work upon renal cells of salamanders that seeretory activity seems 
to be lessened during mitosis. Possibly the more compact condition 
of the chromatin when gathered into chromosomes during mitosis is 
less advantageous for the chemical activity of the chromatin. But 
if this is the whole reason for all other nuclei hastening to com- 
plete the mitotic phenomena when once they are begun, it is diffi- 
cult to see why Opalina mitotica alone, of all known animals and 
plants, should refuse this advantage and permit its nuclei to rest 
in mid-mitosis. The fact that it uses predigested food and so its 
nuclei are less active in enzyme formation is not a sufficient ex- 
planation, for this is equally true of many other intestinal parasites 
whose mitosis does not remain incomplete. 
Growth is oceurring in these Opalinas with anaphase nuclei 
for in individuals of all sizes the same condition of the nuclei is 
seen. The nuclei must be chemically active. 
Is there any regard in which the nuclei of Opalina are peculiar, 
and if so can any suggestion be obtained from this peculiarity, that 
may throw light on our question? As described in a previous 
paper (Mrrcatr 1909), the whole mitosis of Opalina is peculiar. 
There is in the Opalinas no trace of centrosome or of definite achro- 
matic spindle fibres. The irregular mitotic spindle in this genus is 
formed by strands of chromatin, as it were linear, branching pseu- 
dopodia from the chromosomes. The migration of the chromosomes 
to the poles seems to be due partly to the thickening and conse- 
quent shortening of the chromatin spindle fibres which run from the 
chromatin to their attachment to the nuclear membrane at the poles 
of the nucleus (]. e.: “this membrane, we remember, persists, not dissappe- 
aring at any stage of mitosis”), and partly to an absorption of these 
spindle fibres into the chromosomes, the chromosomes absorbing the 
spindle fibres as they crawl along these fibres toward the poles. 
There is no mechanical need of any centrosome to serve as a point 
of resistence or attachment for the spindle fibres, for the very tough 
nuclear membrane serves this purpose. The daughter chromosomes 
merely crawl apart from one another. 
Is it anything connected with this absence of centrosomes and 
achromatic spindle which may explain the delay in completing the 
mitotic process? Alveolar achromatic material is present in the 
nucleus of Opalina, oceupying the whole inner portion of the nucleus, 
