730 THE AMERICAN NATURALIST. [Vor. XXXIX. 
times be recognized as deeply staining globules (the so called 
extranuclear nucleoli). 
There is left for our consideration that group of kinoplasmic 
structures termed centrosomes, centrospheres, and blepharo- 
plasts which, when accompanied by radiations, are called asters. 
Some authors regard these structures as homologous and believe 
them to be present in one form or another as permanent organs 
of the cell in certain types (see discussion of Ikeno, :04). 
Against this view stand the well established facts of an increas- 
ing list of forms, both animals and plants, in which these struc- 
tures unquestionably arise de novo at certain periods in the cell’s 
history. To the author this evidence seems insurmountable and 
he cannot believe that the aster is in itself a permanent organ 
of the cell. We shall not take up the subjects of relationships 
here for such discussions have proved of little profit except in 
special cases where the various types of structure are found in 
closely related forms or in the same life history, and these have 
scarcely been studied at all. We know so little about the rela- 
tionships in the thallophytes, where relationships must be sought 
if present at all, that a satisfactory treatment of the subject is 
hardly possible at present. One point seems to have escaped 
attention.in the writings of those who have discussed the cen- 
trosome problem. The active elements of the asters are not the 
central structures (centrosomes, centrospheres, or blepharoplasts) 
but the fibrillae which play such important parts as spindle fibers 
or cilia. This fibrillar condition of kinoplasm has a fixed place 
in the cycle of cell division appearing with each mitosis and at 
the time of cilia formation, but the fibrille are not permanent 
structures of the cell. There is some evidence that the centro- 
somes, centrospheres, and blepharoplasts are merely regions for 
the development and attachment of these fibrille and as such 
may stand as the morphological expression of fibrillze-forming 
dynamic centers rather than as organs which actually induce the 
development of fibrille. 
