Olive. Mitotic clivision of tlie nuclei of tlie Cyanopliyceae. 
23 
Splitting of this double spireme into segments to form chromo- 
somes; tlie process appears to be rather merelv a concentration, 
or rounding up into small particles, of chromatin substance, tlius 
resulting in tlie formation of minute, spherical, or soraetimes 
irregularly shaped granules, ivliicli remain imbedded in tbe achro- 
niatic material. Tlie term „segmented spireme“ lias been applied 
to sucb a condition (Wilson 00, p. 67). We are justified in 
calling tlie minute clmomatin granules tliemselves, in such a seg¬ 
mented spireme, the cliromosomes, by tbe fact that tbeir number 
is constant in tbe cebs of plants of tbe sanie species. 
It can bardly be doubted tbat a longitudinal Splitting of 
tbe ebromosomes occurs, altliougb tbis is a point very difficult 
to determine witb absolute certainty. Tbe middle cells of fig. 8 
seem to afford proof for sucb a conclusion. In tbe lotver of tbe 
two cells, tbe chromatin granule at tbe extreme left appears to 
be double, whbe throughout tbe rest of tbe nucleus, tbere is but 
one row of granules. In tbe cell above, tbis doubbng bas gone 
on to a farther extent. so tbat at botb sides of tbe central bodv, 
Ave can see a double row of dark granules. Et^en rnore indis- 
putable evidence is furnisbed by fig. 13. in which only tbe un- 
differentiated, deeply stained nuclear figure is sbotvn. In tbis 
figure, in eacb of tbe Iavo cells, it tvill be noticed tbat tbe nu¬ 
clear bocly is deeply dfvided equatoriahy by tvalls which batm 
groAvn in front tbe outside tvalls. Furtber, it avüI be seen tbat 
a new Splitting is beginning at tlie edges of tbe daughter central 
bodies of tbe two contiguous daughter cebs. In tbe two farthest 
separated, Ave see no sucb spbtting at tbe ends. Before tbe wall 
first formed bas completely divided tbe ceb, a new dreision bas 
tbus begun and a neAA^ wab is growing in to meet tbis plane of 
fission. Such an unparabeled example of rapid dhusion occurs, 
so far as I baA T e observed, only in tbe two langer species of 
Oscillatofia, 0. princeps and 0. Froelichia. Careful examination, 
especiaby in preparations not so deeply overstained, reA^eals tbe 
fact tbat a cliromatin granule lies at eacb outer extremity of 
tbe Splitting portion of tbe central body, whereas only one sucb 
dark bodA^ is eAudent in an undivfided end. We are tkeref'ore 
«y 
justified in tbe conclusion tbat eacb cliromatin granule in a mi- 
totic figme must undergo fission in a plane parabel to tbe sub- 
sequent plane of drvision of tbe ceb, tbus agreemg witb tue 
corresp on ding plienomenon of spbtting and Separation of cliro- 
mosomes in bigber plants. 
Kobbs curious scheine for accompbsldng tbe equal diAÜsion 
of bis ebromosomes (03, Taf. k, fig. 12) does not bear mueh re- 
semblance to tbe corresponding process occurring in tbe bigber 
plants. Tbis sebeme fabs to provide for a longitudinal spbtting 
of tbe spireme thread. Aidiich. instead, is twice transversely seg¬ 
mented, a pbenomenon Avhich, so far as I am aware, bas been 
nowhere eise obseiwed in tbe organic kbigdom. Tbe first break- 
ing up of bis eoiwoluted tbread restbts in a dkfision into six 
extremely long straigbt ebromosomes. arranged parabel to tbe 
