164 TRANSACTIONS OF THE [may 11, 
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with the various fixing agents employed. Apart from this my 
special object has been to determine whether that structure 
commonly known as the centrosome, 7. e., the small dark stain- 
ing body at the poles of the division figure, is a permanent per- 
sistent organ, handed down from one cell division to the next, 
or a transitory structure present only during karyokinesis, dis- 
appearing iater and re-formed at the next division. As will be 
seen, my results show conclusively that so far as T’halassema is 
concerned, the former is the correct alternative; and on this 
point my results agree with those of van Beneden and Boveri 
(Ascaris), Mead (Chetopterus), Wheeler (Myzostomum), and 
others who have more or less definitely attained the same result. 
The present paper deals principally with the achromatic 
structures; the history of the chromatin the author hopes to 
discuss in detail in a future work. 
The material included series fixed with picro-acetic and sub- 
limate-acetic, and a few stages with pure sublimate, and with 
Merkel’s Fluid. Of these the best results were given by picro- 
acetic, which gives, in most cases, faultless preservation of all 
the structures. In the series fixed by sublimate acetic, certain in- 
teresting differences are seen, a description of which. will be de- 
ferred until the normal history of the centrosome has been con- 
sidered in detail. 
The eggs were imbedded in paraffine, cut into sections 25h 
thick, mounted and stained on the slide by Haidenhain’s Iron 
Hematoxylin, followed in a few cases with Congo Red to dif- 
ferentiate the reticulum of the centrosphere. 
I desire to express my indebtedness to Professor E. B. Wilson 
for the numerous courtesies he has extended me during the 
progress of the work, and my sincere appreciation of his advice 
and encouragement. 
THE EGG CENTROSOME. 
The earliest trace of the egg centrosomes that I have so far 
been able to detect was in preparations from eggs fixed about 
ten minutes after fertilization. They then appear as two minute 
dark staining granules, already distant about 90°, situated close 
to the nuclear membrane which is still intact though showing a 
slight invagination, folding, or at least a flattening next the cen- 
trosomes. This is probably caused by inwardly growing rays. 
At this stage the centrosomes are indistinguishable from the 
surrounding cytoplasmic granules, save for the minute few and 
short rayed aster focused at each. This fact renders the ques- 
tion of the origin of the centrosome extremely difficult if not. 
