1912.] NATURAL SCIENCES OF PHILADELPHIA. 131 



Edwin G. Conklin, Ph.D.: "Experimental Studies in Nuclear and 

 Cell Division." Illustrated.* 



During several seasons extensive experiments were made on the 

 segmenting eggs of Crepidala plana. These experiments include a 

 study of the influence on nuclear and cell division of hypertonic 

 and hypotonic sea water, of ether, alcohol, etc., of the lack of oxygen, 

 of carbon dioxide, of the electric current, and of pressure and shaking. 

 The following general conclusions may be drawn from this work: 



1. Under the same treatment the effects on cell division may be 

 extremely varied, owing, probably, to the different stages acted upon. 



2. A dividing cell is much more easily disturbed or rendered 

 abnormal than is a resting one; the mitotic figure in particular is 

 very easily altered and most of the abnormalities observed arise 

 from this source. 



3. The earlier stages of cleavage are much more easily altered than 

 are the later ones. 



4. Certain general abnormalities occur after the most varied 

 treatment, e.g., the general result both of concentration and of 

 dilution of sea water is to produce polyasters and to prevent the 

 cleavage of the yolk. 



5. On the whole, the results of the hypertonic solutions are the 

 same whether the} r are produced by evaporation of the sea water or 

 by addition of NaCl, MgCl, or KC1 to sea water; in short,, these 

 salts exert no specific action on cell division. 



6. The most general modification of the mitotic figure is the 

 production of polyasters, multipolar spindles, and as a consequence, 

 multiple nuclei. In many cases the cells are filled with asters and 

 irregular mitotic figures during division, while in the resting stage 

 they are filled with equally numerous resting centrosomes and nuclei. 



7. The movements of the chromosomes are in many cases inter- 

 rupted, so that they remain scattered along the spindle, while the 

 cytoplasmic movements are frequently stopped or altered. 



8. In some cases the achromatic portion of the nucleus is separated 

 from the chromatic part, and the two may persist side by side during 

 the resting stage of the cell; in the division stages the achromatic 

 nuclei give rise to asters, the chromatic to chromosomes and both 

 may divide indefinitely, giving rise to large numbers of chromatic 

 and achromatic nuclei. 



9. The most general modification of the division of the cell body 

 is the suppression of the cleavage of the yolk; this occurs in practi- 

 cally all the experiments ; at the same time the cleavage may proceed 

 more or less regularly in the protoplasmic portion of the egg. In 

 normal eggs the first and second cleavages divide the yolk into four 

 equal cells (the macromeres) and from each of these three small 

 cells (the micromeres) are budded off. 



10. If the yolk remains undivided it gives rise in certain cases to 

 three micromeres, which have the characteristics of those formed 



* An asterisk after the title of the paper indicates that it is published in the 

 Commemorative Volume of the Journal of the Academy (XV) . 



