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H. E. Jordan 
nor later can centrosomes be demonstrated. The centrosome itself 
seems then to represent simply a transient metabolic phase of karyo- 
kinetic activity. And the aster itself, contrary to Geifpin’s State- 
ment for Zirphaea^ seems to be the eflfect rather than the cause of 
cell activity. 
Cumingia differs also in another respect from Zirphaea as des- 
cribed by Griffin. In Zirphaea the aster of the central pole of the 
second polar spindle is described as persisting in relation to the fe- 
male pronuclens ; while another appears in relation to the male pro- 
nncleus. Griefin seemed nndecided as to the origin of the cleavage 
aster. In Cumingia no aster remains in Connection with the female 
pronuclens. Nor is one seen in connection with the male pronuclens. 
At the proper time the amphiaster simply seems suddenly to appear 
and to be about as intimately related to one pronuclens as to the 
other. 
Another interesting point is the absence of nucleoli in the pro- 
nuclei. In this respect Cumingia differs sharply from some of the 
echinoderms. Nor do nucleoli appear even in the later cells of the 
blastula. Mitosis seems to proceed too rapidly for the formation of 
these structures. 
The evidence from a study of the egg of Cumingia indicates 
with especial clearness that the egg-cell as a whole is the "unit” 
and the "dynamic center”, and that the various strnctural featnres, 
nucleolus, chromosomes and centrosomes are simply the effect or 
transient morphologic expressions of underlying vital activities. 
Bibliography, 
Bonnevie, K. ’08. Chromosomenstudien. I. Arch. f. Zellf. Bd. 1. Heft 2 and 3. 
Boveri, Th. '90. Zellenstudien. UI. Über das Verhalten der chromatischen Kern- 
substanz bei der Bildung der Richtungskörper und bei der Befruch- 
tung. Jena 1890. 
CoNKLix, E. G. ’02. Karyokinesis and cytokinesis in the maturation, fertili- 
zation and cleavage of Crepidula. Journ. Acad. Rat. Sei. Phila. 12:1. 
Davis, B. M. ’05. Studies on the plant cell. Am. Nat. Vol. 39. 
Foot, K. and Ströbele, E. C. ’09. The Nucleoli in the Spermatocytes and 
Germinal Vesicles of Euchistus variolarius. Biol. Bull. Vol. XVI. 
No. 5. 
Goldschjiidt, R. 08. Ist eine parallele Chromosomenkonjugation bewiesen? 
Arch. f. Zellf. Bd. 1. Heft 4. 
Griffin, B. B. Studies on the maturation, fertllization, and cleavage of Thalas- 
sema and Zirphaea. Vol. XV. 1898. 
