188 MEAD. [Vou. XIV. 
The multiple asters in the egg of Cheetopterus are certainly 
normal; they are demonstrable in the “ving eggs, are brought 
out by various reagents, are a constant feature of every egg at 
a certain stage of its development, and always undergo a con- 
stant and continuous series of consecutive changes. Therefore, 
as far as the phenomena in Cheetopterus prove the free forma- 
tion of the centrosome at all, they prove it in the normal 
aster; and the same can be said of Reinke’s observation. 
(b) Zhe Function of the Centrosomes in Fertilization. 
The classic papers of Boveri ('87,'91) and Fol (91) formulated 
and brought into prominence twodistinct theories of fertilization: 
that of Boveri rests upon thesupposition that thecentrosome is the 
dynamic centre of the cell and initiates cell-activities. It implies 
also that the centrosome is a permanent and ultimate cell-organ, 
handed down from one generation to another by means of the 
spermatozoon. The gist of the theory appears in a paragraph 
from his earlier paper: ‘‘ The ripe eggs possess all the organs 
and qualities necessary for division, excepting the centrosome, 
by which division is initiated. The spermatozooén, on the other 
hand, is provided with a centrosome, but lacks the substance in 
which this organ of division may exert its activity. Through 
the union of the two cells in fertilization, all the essential 
organs necessary for division are brought together; the egg 
now contains a centrosome which, by its own division, leads the 
way in the embryonic development.”’ He writes also: “The 
end of fertilization is the union of the germ nuclei and the equal 
distribution of their substance, while the active agent in this 
process is the centrosome.... It is the centrosome alone that 
causes the division of the egg, and is, therefore, the fertilizing 
element proper.”’ To these conclusions Wilson subscribes.! 
Fol maintained, on the other hand, that, in fertilization, the 
centrosomes of the cleavage-amphiaster arise by the fusion of 
sperm-centrosomes and egg-centrosomes, just as the cleavage- 
nucleus is formed by the union of the sperm-nucleus and the 
egg-nucleus. The centrosome at either pole of the amphiaster 
1 Wilson, “ The Cell,” p. 140. 
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