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IS THE BLEPHAROPLAST A CENTROSOME. fi 
that any cell organ, which never forms the center of an aster at the 
pole of the spindle, has been considered by any investigator as the 
homologue of a centrosome. An exception, of course, must be made 
in the case of the blepharoplasts of Zama, Cycas, and Ginkgo, which 
are under discussion, if we accept the statement that they are at the 
poles of the spindle. The blepharoplasts of JJarsi/ia, according to 
Belajeff’s investigations, are located at the pole of the spindle, but, 
judging from his figures, they are not located in the center of an 
aster. 
In regard to the second proposition, it may be stated that in all of the 
well-worked-out cases in plants where centrosomes or centrospheres 
occur, as in Sphacelaria, Dictyota, Fucus, Hepatic, etc.. the centro- 
some is of prime importance in spindle formation. There are, of course, 
cases which have not been thoroughly studied where this is not known 
to be the case. While this statement would hold true in general with 
animal cells, the writer is not sufficiently familiar with the literature 
to discuss the possible exceptions. 
As to the third proposition there is a very great difference in differ- 
ent cases. The original idea of Boveri that the centrosome is a neces- 
sary and permanent sv7 generés organ of the cell, passing from cell to 
cell in division, has probably been abandoned by all investigators of 
the present day. It is claimed in various plants and animals to origi- 
nate dz novo in the cell, or at least become visible only at certain stages 
and in certain tissues. However, in all cases of genuine centrosomes 
known to the writer, they occur regularly in the cell divisions of cer- 
tain tissues and seem to be mainly concerned with the spindle forma- 
tion and division, having this as their prime if not sole and only function. 
Considered in comparison with the above-described attributes of a 
centrosome, the blepharoplasts of Zamia, Cycas, and Ginkgo would 
seem to be very distinctorgans. In Zama the blepharoplast is located 
‘in the center of a very noteworthy aster, but when the spindle is 
formed there is found to be no connection between this and the 
blepharoplasts, which are located some distance outside the pole of the 
spindle. The same feature is very noticeable in Cycas, judging from 
Ikeno’s figures 25a and 25b (70), and in Ginkgo, judging from Hirase’s 
figures 18 and 19 (62). 
The blepharoplast of Zama has no discernible part in spindle forma- 
tion, and it is certainly not a spindle-forming and division-directing 
organ. In no stage of the division have the spindle fibers any connec- 
tion with it. The same can be said of Cycas and Ginkgo, so far as 
can be told by the investigations of Ikeno and Hirase. In Ginfgo in 
particular Hirase (62, fig. 18) figures an aster at the pole of the spindle 
inside of which a centrosome should be located, if present. The 
blepharoplast with its radiations, however, is located in the cytoplasm 
outside of this, the rays having apparently no connection. 
