264 M. M. Mercavr 
comparable. In Ascaris and the salamander the condition in the 
telophase seems to be unrelated to the true splitting of the chromo- 
somes, which occurs during the next mitotic cycle, a resting stage 
intervening. This comparison with Ascaris and the salamander adds 
more doubt to the already very doubtful interpretation of the ap- 
pearance in the telophases of Opalina as indicating a splitting of the 
chromosomes. 
CauKins & Cun (1907) found that splitting of the chromosomes 
occurs in the two maturiation divisions of Paramaecium, but not in 
the third division by which the conjugating nuclei are formed. The 
ordinary vegetative divisions of Paramaecium have not been so stu- 
died as to show whether splitting of the chromosomes occurs in 
them or not. Neither Hampurcer (1904) nor Cauxins & Cunt show its 
presence in the nuclear divisions immediately following conjugation. 
These conditions suggest the possibility that in Opalina the matu- 
ration divisions may differ from the vegetative divisions and that 
splitting of the chromosomes may be found in the maturation di- 
visions. I have used for the most part, with the minute individuals 
of Opalina in the spring, methods which do not show the finest de- 
tails. My study of carefully stained sections has not yet shown in 
detail the phenomena of maturation. Another spring’s work will 
propably be necessary to determine this interesting point. 
An alternative explanation of the mitosis. 
The alternative interpretation of the nuclear division in Opalina 
as a very primitive mitosis in which there is no longitudinal splitting 
of the chromosomes needs further development. We have seen that 
the chromatin masses (properly called chromosomes only in certain 
conditions) are always branched, their branches being connected to 
form a network just beneath the nuclear membrane; and we have 
also seen that some of the fibres of the network are attached to the 
nuclear membrane at each of the two poles of the nucleus. This 
attachment of the fibres is very clearly seen when the spindle is 
well developed. The manner in which the nucleus constricts in each 
mitosis until the membrane at the equator of the nucleus pinches 
and holds the fibres of the spindle, explains the fact that these 
fibres are attached to the membrane only at the two poles. One 
night conceive each longitudinal chromatin fibre of the mitotic 
spindle in Opalina, with all its branches and with the two chro- 
matin masses upon it, as forming one unit, the units being in con- 
