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Nachdruck verboten. 



Centrosoiiie and Sphere in the Maturation, Fertilization 

 and Cleavage of Crepidula. 



By Edwin G. Conklin. 



Mit 8 Diagrams, 



(From the Zoological Laboratory of the University of Pennsylvania). 



The present paper is a brief summary of that portion of my 

 work on Karyokinesis and Cytokinesis in Crepidula and other marine 

 Gasteropods, which refers to the structure of the centrosome and 

 sphere. The complete work will appear soon in the Journal of 

 Morphology. 



I. Maturation. 



Centro somes. In the early prophase of the first maturation 

 the centrosomes and central spindles lie outside of the germinal vesicle, 

 the membrane of which is at this time intact. The centrosomes are 

 minute points, too small to be measured and so small that their finer 

 structure could not be determined. They are surrounded by small 

 spheres through which the astral rays run to be inserted in the cen- 

 trosomes (Diagram A, Fig. 1). 



In the early metaphase each centrosome is an irregular body 

 consisting of closely connected granules which surround a central clear 

 area (Dia. A, 2, 3). At this stage the centrosomes entirely resemble 

 those which Lillie^) has described in Unio, except that the granules 



1) LiLLiE, Centrosome and Sphere in the Egg of Unio. Zoological 

 Bulletin, Vol. 1, No. 6, 1898. 



