KARYOKINESIS AND CYTOKINESIS IN THE MATURATION, FERTILI- 

 ZATION AND CLEAVAGE OF CREPIDULA AND 

 OTHER GASTEROPODA. 1 



By Edwin G. Conklin, Ph.D. 



I. 



Introduction. 



Cell division, in a broad sense, includes not only nuclear division and the separa- 

 tion of daughter cells, but also all the phenomena which lead up to these processes 

 and which follow them; the terms Karyokinesis (Schleicher '78) and Cytokinesis 

 (Whitman '87) are used in this paper to include these nuclear and cytoplasmic 

 activities of the entire cell-cycle from one division to the next. Flemming ('82) has 

 objected to the term Karyokinesis on the ground, among others, that nuclear move- 

 ments are not characteristic of indirect division. But in view of the extensive 

 movements of both nuclei and cytoplasm, which occur in the cell divisions described 

 in this paper, the terms Karyokinesis and Cytokinesis have peculiar appropriateness. 2 



The phenomena of cell division still include an extraordinary number of dark 

 problems, in spite of the fact that " all the search-lights of the biological sciences 

 have been turned upon the cell." Confusion and contradiction exist as to the nature 

 and metamorphoses of the centrosome and central spindle, the origin and fate of the 

 amphiaster, the characteristics and history of the attraction sphere, the existence or 

 non-existence of a specific substance (Archoplasm, Kinoplasm, etc.) whose primary 

 function is the division of the cell. Still less complete is our knowledge of the inter- 

 relation of nucleus and cytoplasm during the various phases of division, of the 

 phenomena and significance of the movements of cells and cell constituents and ol 

 the chemical, physical and physiological principles involved in the division of nucleus 

 and cell body. 



In the early development of the egg, cell divisions have a peculiar interest 

 because of their bearings on problems of heredity and differentiation. Here are 

 found phenomena of the most general occurrence and of the deepest significance, viz.: 

 the maturation, fertilization and cleavage of the egg and the early differentiation of 

 the embyro. The bearings of the phenomena of maturation and fertilization upon 



1 From the Zoological Laboratory of the University of Pennsylvania. 



2 On the other hand Flemming's term mitosis commends itself because of its brevity, and it is 

 frequently employed throughout this paper. 



1* JOTJRN. A. N. S. PHILA., VOL. XII. 



