

554 CELL DIVISION IN EGGS OF CREPIDULA. 



meres may be abnormal in position. With a stronger current (or more perfect 

 penetration) chromatin and chromosomes may be clumped into masses or even 

 completely dissolved, while the spindles and asters may be preserved in some 

 cases or dissolved in others. With a stronger current (or more perfect 

 penetration) cytoplasm and yolk may be stratified and nuclei and spindles dis- 

 placed by convection currents. There is no indication that the poles of spindles 

 bear charges differing in sign from the chromosomes, or that spindle fibers or 

 astral rays represent lines of force in an electric field, or that the movements of 

 chromosomes into or out of the equatorial plate are caused by electric charges 

 carried by the chromosomes and centrosomes. (Figs. 68-93; pp. 518-524.) 

 5. Increase of temperature from 10° to 16° above that of normal sea water, 



if only for % hour, leads to profound modifications of cell division. The most 



general effects are: (1) Reduction of surface tension, with consequent irregu- 

 larities in the contour of eggs and changes in the type of cleavage. (2) With- 

 drawal of astral rays and segregation of archiplasm in the spindle area and along 

 the walls between cells. (3) Great changes in the orientation and structure of 

 mitotic figures ; loss of spindle fibers and centrosomes ; scattering of chromosomes 

 and formation of numerous karyomeres. (Figs. 94-99; pp. 524-525.) 



In eggs kept near the freezing point all divisional phenomena are soon stopped; 

 after 14-16 hrs. on ice the centrospheres, during resting stages, become bounded 

 by a definite membrane and look like faintly-staining nuclei ; after 40 hrs. on ice 

 centrospheres break up into coarse, chromatic granules, which may be homolo- 

 gous with mitochondria. (Figs. 100-105; pp. 525-526.) 



6. In 1 per cent, and 2 per cent, solutions of ether in sea water cell division 

 proceeds with few modifications; in 3 per cent, solutions all karyokinetic and 

 cytokinetic movements cease and cell division is suppressed, archiplasm is with- 

 drawn into the central portion of the aster and into division walls between cells, 

 chromatin is clumped in resting nuclei, chromosomes are scattered along the 

 spindles, and spindle fibers are indistinct or absent. (Pp. 526-527.) 



7. In water in which the oxygen tension is reduced by boiling, or by running 

 a current of hydrogen through it, cell division is greatly retarded or completely 

 stopped , but cleavages are normal in type as far as they go ; resting nuclei and 

 nucleoli become larger than usual during the long interkineses, and the chromatin 

 is clumped into a nucleolus-like mass ; centrospheres lose their definite outlines 

 and consist of coarse, widely-scattered granules; spindle fibers, chromosomes and 

 centrosomes remain distinct, but astral radiations disappear, the archiplasm 

 being drawn into the central figure of the amphiaster and into the division walls 

 between cells. (Figs. 106-118; pp. 527-529). 



8. Addition of C0 2 to sea water causes local reductions in the surface tension 

 of both cells and nuclei, whereby their surfaces become lobulated ; also tne 

 positions and directions of mitotic figures and of the resulting cell divisions are 

 altered. (Figs. 119-131; pp. 530-532.) 



9. Hypotonic sea water may induce polyspermy; isolation of blastomere , 







