CELL DIVISION IN EGGS OF CREPIDULA. 



III. Effects of Pressure. 



561 











Free 





No. 



Stage. 



Experiment. 



Duration. 



in Sea 

 Water. 



Eesults. 



849 



1-2 cells. 



Pressed between 

 slides. 



4 hrs. 



13 hrs. 



16-30 cells; many abnormal cleavages, yolk 

 cleavage being increased in some egg and 

 suppressed in others, depending upon the 

 axis of pressure. 



850 



1-4 cells. 



Pressed between 

 slides. 



5% hrs. 



6 hrs. 



2-24 cells; many cleavages abnormal in size 

 and direction; yolk cleavage may be 

 increased or suppressed. 



851 



1 cell. 



Pressed between 

 slides. 



8 hrs. 



11 hrs. 



20-24 cells; 1, 2, or many macromeres due to 

 suppression or increase of yolk cleavage; 

 polyasters and multiple nuclei. 



852 



2-4 cells. 



Pressed between 

 slides. 



13 hrs. 



4 hrs. 



8-30 cells; similar to preceding; some blasto- 

 meres isolated. 



853 



1-4 cells. 



Pressed between 

 cover glasses. 



Ui hrs. 



3 hrs. 



4-30 cells; many normal eggs; abnormal forms 

 like those in No. 852. 



854 



1-4 cells. 



Pressed between 

 cover glasses. 



18 hrs. 



4 hrs. 



1-30 cells; in some eggs all cleavage sup- 

 pressed; others show abnormal forms similar 

 to preceding. 



884 



1-2 cells. 



Pressed flat 

 under cover. 



3Jhrs. 



12i hrs. 



1-30 cells; many isolated blastomeres, frag- 

 mented and degenerating eggs. 



885 



1-2 cells. 



Pressed between 

 slides. 



4 hrs. 



10J hrs. 



20-30 cells; yolk cleavage suppressed (with 

 multiple nuclei) or increased (with multi- 

 plication of macromeres). 













886 



4 cells. 



Pressed between 

 slides. 



12£ hrs. 



1J hrs. 



Many fragmented and degenerating; abnor- 

 mal cleavages similar to preceding. 



893 



24 cells. 



Pressed between 

 slides. 



4 hrs. 



Jhr. 



Few modifications. 



894 



lcell. 



Pressed between 

 slides. 



4 hrs. 



Jhr. 



1-2 cells; few modifications. 



895 



4 cells. 



Pressed out of 

 capsules. 



4 hrs. 



f hr. 



Few eggs; few modifications. 



896 



30-40 cells. 



Pressed in cap- 

 sules. 



4 hrs. 



2 hrs. 



Few modifications; eggs faded. 



897 



1 cell. 



Pressed out of 

 capsules. 



4 hrs. 



£hr. 



Few eggs and much faded. 



898 



16-24 cells. 



Pressed in cap- 

 sules. 



4 hrs. 



2 hrs. 



Ca. 30 cells; few modifications. 



899 



16-24 cells. 



Pressed in cap- 

 sules. 



4 hrs. 



hrs. 



24-30 cells; eggs packed together and abnormal 

 in form. 



900 



1-24 cells. 



Pressed out of 

 capsules. 



4 hrs. 



hrs. 



1-24 cells; macromeres may be abnormal in 

 number, size and position. 



901 



1 cell. 



Pressed out of 

 capsules. 



4 hrs. 



hrs. 



1—4 cells; modifications similar to preceding 

 Fig. 48. 



902 



4-16 cells. 



Pressed out of 

 capsules. 



4 hrs. 



2 hrs. 



4-20 cells; similar to No. 900. 



903 



lcell. 



Pressed out of 

 capsules. 



4 hrs. 



2 hrs. 



1-4 cells; modifications similar to No. 900. 



904 



1-8 cells. 



Pressed in cap- 

 sules. 



4 hrs. 



2 hrs. 



1-16 cells; macromeres and micromeres may 

 be abnormal in number, size and position. 

 Fig. 55. 



905 



1 cell. 



Pressed out of 

 capsules. 



4 hrs. 



2 hrs. 



1-8 macromeres; few eggs. 



906 



1-8 cells. 



Pressed out of 

 capsules. 



4 hrs. 



2 hrs. 



1-20 cells; a few abnormal cleavage forms. 

 Fig. 30. 



907 



lcell. 



Pressed out of 

 capsules. 



4 hrs. 



2 hrs. 



1-4 cells; unequal and non-synchronous divi- 

 sions of macromeres. 



908 



1-24 cells. 



Pressed out of 



capsules. 

 Pressed in cap- 



4 hrs. 



4 hrs. 



1-30 cells; exovates on some macromeres. 



909 



8-24 cells. 



4 hrs. 



4 hrs. 



30-40 cells; almost all normal. 







sules. 









37 JOURN. ACAD. NAT. SCI. PHILA. VOL. XV. 



