258 M. M. Mercarr 
the nucleus is in the chromosomes. Soon the chromosomes begin 
again to send out processes and the chromatin network of the resting 
nucleus is formed. The whole migration of the chromosomes and 
the reformation of the chromatin network suggests comparison with 
the movements of a reticulate foraminiferan. All the chromatin 
seems to be active in this movement. 
No explanation of the migration of the daughter chromosomes 
as dependant upon some repulsion between them, connected with their 
splitting, can apply here, for no such splitting occurs in the equatorial 
plate stage or immediately preceeding it. The splitting, if it occurs 
at all, is found in the telophases of mitosis, after, not before, the 
migration of the daughter chromosomes. 
A chromosome cannot crawl upon nothing any more than can an 
animal. There must be some resistant substance upon which the 
moving chromosomes can advance. The resistant substratum in this 
case seems to be the alveolar achromatic material which fills the 
center of the nucleus, and whose alveoles with their delicate walls 
and contained liquid seem to furnish the necessary resistence for the 
movements of the chromosomes and their pseudopodia (chromatin 
fibrils). The attachment of the spindle fibres to the nuclear mem- 
brane also, of course, aids in these movements. 
What causes the chromosomes to arrange themselves at first in 
the equatorial third of the nucleus and later to crawl to the poles 
of the nucleus, and what causes the changes in the form of the 
nucleus, are questions whose answer the conditions in Opalina do 
not help us to approach. 
Such a mitotic division as we see in Opalina, in which all parts 
of the nucleus seem to be active, membrane. chromatin and achromatin 
all sharing by active growth and movement, seems not only less 
specialized than the mitosis of higher forms, but also less removed, 
at least mechanically, from amitotic division, in which also probably 
all parts of the nucleus share by active movements. The presence 
of centrosomes in a cell allows the nuclear membrane and the chro- 
matin and, in the most highly developed mitoses, the achromatic 
foam of the nucleus also, to be less active. 
The EE of the nuclei and the planes of division of the 
nuclei and of the body. 
The nuclei of the binucleated Opalinae are always somewhat 
elongated, their two poles being always clearly recognisable. This 
