THE ORIGIN OF THE CLEAVAGE CENTROSOMES. 
KATHARINE FOOT, Evanston, Illinois. 
DurinG the past two years the weight of authority has 
greatly increased in favor of the conclusion that the cleavage 
centrosomes are of spermatic origin. 
These centrosomes are asserted to be the daughter centro- 
somes of the so-called male centrosome, and this is assumed to 
originate from the middlepiece of the spermatozo6n, —to be 
of the very substance of which the middlepiece was formed. 
The phenomena of fertilization in the egg of AUolobophora 
foetida do not sustain this view; they suggest that this centro- 
some has the same origin as the so-called egg centrosome, 
and that both are cytoplasmic elements, of like origin and 
constitution. 
The sperm attraction sphere and the fertilization cone have 
several points in common; both structures appear to be 
dependent, not alone upon the entrance of the spermatozoon, 
but also upon a definite stage of maturation reached by the 
egg ; for I have never found a cone after the first polar body is 
constricted off, nor a sperm attraction sphere before the ana- 
phase of the first spindle, no matter how far the spermatozoon 
may have penetrated into the egg ; both appear to be formed 
of substances not confined to the structures themselves, but 
belonging to the entire cytoplasm.? 
These observations suggest that both the cone and the 
attraction sphere are expressions of a definite effect produced 
upon the cytoplasm by the entrance of the sperm, the phenom- 
1 In the summer of 1895 I differentiated from the cytoplasmic network a sub- 
stance (archoplasm) which is present in the attraction spheres, in the fertilization 
cone, in the spindle, and throughout the cytoplasm (see Journ. of Morph., vol. 
XII, Plate I). Recently I have differentiated the microsomes and centrosomes 
from the cytoplasm and archoplasm (Figs. 2, 3, 4, 7,9, 10). These microsomes 
do not appear to be merely thickenings of the cytoplasmic threads ; they appear 
to be morphological elements, many of them scattered throughout the cytoplasm 
in a relatively independent manner, others imbedded in the cytoplasmic network. 
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