No. 2.] CENWTROSOMES IN THE ANNELID EGG. 18 
J 
Watasé’s endeavor to bring into relation the various proto- 
plasmic structures, cyto-microsomes, “centrosomes,” Zzw7schen- 
korper, rod-like “centrosomes” of the pigment-cell, contraction- 
band of the muscle-cell etc., is an attempt to extend, not the 
terminology, but the homology of the centrosome. Which of 
the three concentric structures — centrosphere, centrosome, or 
centriole — at the centre of the aster in Echinus (Boveri) is the 
morphological equivalent of the centrosomes of Strongylocen- 
trotus (Fol), the large centrosphere of Toxopneustes (Wilson), 
the scattered centrosomes in the leucocyte (Heidenhain), the 
centrosphere-like centrosomes of Crepidula (Conklin), the minute 
centrosomes of Myzostoma (Wheeler), Chzetopterus (Mead), 
and Thalassema (Griffin), must, terminology aside, remain a 
matter of interpretation based on structural and physiological 
characters. 
It is usually assumed that that structure in the aster which 
persists through the various stages of mitosis is to be consid- 
ered the centrosome, whether it be a large reticular area 
(Crepidula), a minute dot frequently surrounded by such an 
area, or a structure midway between the two (Echinus). On this 
principle Wilson, in his paper on the “ Archoplasm, Centro- 
some, and Chromatin of the Sea-urchin Egg,” raises his pre- 
viously described “ central mass”’ of the aster of Toxopneustes to 
the morphological value of a centrosome, though he has since, 
on other grounds, altered this interpretation. ‘‘ What, then, 
shall we identify in the sperm-aster of Toxopneustes as the 
‘centrosome’ in Boveri's sense, z.¢., as the structure that divides 
to form the dynamic centres of the ensuing cleavage? I think 
the only structure that can answer to this definition is the 
central mass of the aster, z.e., the substance of the original 
middle-piece, without regard to its subsequent morphological 
differentiation.” 
It was on precisely these grounds that, in a preliminary paper 
on the “ Fecundation of Chzetopterus,”’ I identified the minute 
dark granules in the centres of the asters as centrosomes, and 
endeavored to show that the centrosomes which were developed 
in connection with the sperm-aster persist and, by successive 
divisions, furnish the centrosomes of each cleavage-spindle up 
