182 MEAD. [Vou. XIV. 
(a) The Morphological Relation of the Centrosome to the Other 
Organs of the Cell. 
This problem demands consideration of the doubt as to the 
very existence of the centrosome as a definite cell-organ, and of 
the uncertainty as to the zdenzzty of this organ in case it exists. 
The possibility that bodies described as centrosomes are fre- 
quently artifacts does not rest solely upon the negative evidence 
of numerous observers who fail to find centrosomes where they 
might be expected to occur, but upon the fact that similar bodies 
can be produced by the coagulative action of certain reagents. 
The classic centrosomes, which dance the quadrille in the 
egg of Strongylocentrotus lividus (Fol, '91) are not found by 
later workers in the eggsof closelyrelated sea-urchins. Inhis first 
paper on the “ Fertilization of Toxopneustes,” Wilson main- 
tains that in well-preserved material ‘“ there is absolutely noth- 
ing to be identified as a centrosome,” though irregular clumps 
— fortuitous groups of granules—closely similar to those 
described by Fol as “centrosomes ’”’ may be produced by the 
destructive action of picro-osmic acid. Eismond (Azat. Auz., 
X, 7, 8) and others have suggested that the centrosomes or 
“centrioles”’ have been, at least in some cases, produced by 
the clotting action of reagents, and do not represent actual cell- 
organs. But in view of the fact that so many investigators 
have demonstrated the centrosome in many different cells and 
with different reagents, and that in some instances this struc- 
ture can be followed through a constant and continuous series 
of changes, including growth and division, it is safe to maintain 
that the centrosome is an actual organ of the cell. 
While the existence of the centrosome has been established 
beyond a reasonable doubt, there still remains the puzzling 
question of zdentity. Structures widely different in appearance 
have been called centrosomes, and the same structure has been 
designated by this and by various other names. Much confu- 
sion, therefore, arises from the terminology, though the dis- 
crepances can by no means be assigned to this cause alone, for 
there are differences of interpretation in regard to the morpho- 
logical limitations of the structure itself. 
