54 MEAD. [Vou. XIV. 
to the 8-cell stage. Having requested some of my preparations 
for examination, Wilson says in referring to them (AZ/as of 
Fertilization, p. 20): “The central mass of the aster undoubtedly 
contains at this period (early phase of the cleavage-amphiaster) 
one or two deeply staining centrioles, which in this case may 
possibly have the morphological value of centrosomes.” How- 
ever, reéxamination of all the stages with new material supports 
my earlier interpretation that these structures have unquestion- 
ably the morphological value of centrosomes. 
More recently Wilson also has discovered two deeply stain- 
ing “ centrioles’ in the aster of the egg of the annelid Nereis, 
and Griffin, working under his direction, has found the same 
in Thalassema. Griffin has also showed that these granules, 
arising in the sperm-aster, persist through the first cleavage- 
amphiaster, divide and give rise to the centrosomes of the 
succeeding amphiasters. In view of these results, which indi- 
cate that ‘“‘the true centrosome certainly corresponds to the 
central granule or centriole,’ Wilson is inclined to modify again 
his interpretation of the identity of the centrosome, and to 
believe that further research will bring out the “ minute 
central centrosome ’”’ in Toxopneustes, and in all similar cases 
where they appear to be absent. 
I am indebted to Dr. F. R. Lillie for permission to refer to 
some extremely interesting unpublished observations on the 
egg-centrosomes of Unio which, doubtless, will throw a great 
deal of light upon the question of zdentzty. From the stage in 
which it has the appearance of a minute, deeply staining dot, 
the centrosome is traced, step by step, through a metamor- 
phosis in many of whose phases its identity would not ordi- 
narily be recognized. 
The problem of the morphological relation of the centrosome 
to the other organs of the cell involves also the important ques- 
tions of its origin and its persistence. This question, both sides 
of which have the support of eminent authority, has been stated 
by Watasé (94) in the following terms: ‘‘ According to the one 
view (1) the centrosome is a permanent or ultimate organ of 
the cell, an organ sw generis, and coexistent with other organs 
