NOTES ON SPOEOZOA — II. 
181 
to its true significance, namely, as a karyosome, is single and 
relatively large j it is situated at one side of the general 
nuclear substance, apparently extra-nuclear. This large 
karyosome next undergoes unecpial division. The process 
takes place in a particular mauner, which is neither amitotic 
nor yet a well-defined mitosis. This method of division has 
been usefully distinguished by Niigler (22) as “ promitosis.” 
It may be as well to indicate, first of all, what is meant by 
promitosis. Its characteristic feature is that the division is 
initiated and carried out by means of an internal division- 
centre, which itself fii'st divides, the two resulting daughter- 
centres then passsing away from each other, but remaining 
connected by a distinct fibril or axial thread, the centro- 
desmose.” The term “promitosis” was originally applied by 
Niigler to nuclear division taking place in this manner, the 
intra-nuclear division-centre being a “ nucleo-centrosome ” or 
a karyosome. Where the karyosome plays this part, howevei’, 
the true division-centre — certainly in most cases, and perhaps 
always — is an intra-karyosomatic ceutrosome or centriole, 
which initiates the process, although, owing to the intensity 
with which the karyosome usually stains, the centriole itself 
can larely be distinguished, its presence being often only 
actually discernible at some other period in the development 
(cf. below, p. 182). Tortunately, however, the axial fibril or 
centrodesmose connecting the two separated daughter-cen- 
trioles persists often for a long time, even after the division of 
the karyosomatic or nuclear material is completed ; hence it 
is just this stage of the division-process which is most likely 
to be observed. Therefore, where two nuclei (or karyosomes) 
are seen still connected b}'^ a definite centrodesmose, it may be 
safely concluded that the division has been brought about by 
an internal division-centre (centriole), in a promitotic manner. 
It only remains to say that 1 consider the term “promitotic 
division ” can also be applied very suitably to the division of 
a karyosome, where this occurs unaccompanied by, or inde- 
pendently of, the division of the nucleus itself; .Jollos (12) 
has already used the term in this connection. 
