I 



568 



CELL DIVISION IN EGGS OF CREPIDULA. 



1,010 



1,011 



1,012 

 1,013 

 1,014 

 1,015 



1,016 



1,017 



1,018 



1,020 

 1,021 

 1,022 



1-4 cells. 



lcell. 



1-4 cells. 

 2-20 cells. 

 Gastruke. 



1-8 cells 



1-8 cells. 



1 -8 cells. 



1 cell to gas- 



trula. 



1-20 cells. 



1-20 cells. 



2-20 cells. 



36hrs. 



5 hrs. 



6hrs. 

 20 hrs. 

 20 hrs. 

 24 hrs. 



27 hrs 



48 hrs 



48 hrs. 



20 hrs. 

 24 hrs. 

 20 hrs. 



Ohrs. 



Ohrs. 



Ohrs. 

 Ohrs. 

 Ohrs. 

 Ohrs. 



Ohrs. 



Ohrs 



Ohrs 



3 hrs. 



8 hrs. 



9 hrs 



b. In Stoppered Bottles. 



1-4 cells ; cleavage stopped ; eggs smaller than normal, only 120 m in 

 diameter; nuclei large, vesicular, with large nucleoli; centrosomes 

 very large; sphere granules widely scattered. Figs. 106-109. 



1-4 cells ; astral rays withdrawn and spheres very distinct ; otherwise 

 typical. 



1-20 cells, nearly normal. 



2-20 cells ; nuclei large, with chromatin clumped. 



No changes. 



1-30 cells (a few older stages accidentally included) ; big nuclei with 

 chromatin clumped; spindles faint. 



1-20 cells; nuclei large and achromatic; nucleoli large; sphere gran- 

 ules scattered. Figs. 112, 114. 



1-20 cells ; big nuclei and nucleoli ; chromatin clumped ; sphere gran- 

 ules scattered. Figs. 113, 117. 



1 cell to gastrula; similar to preceding; cleavage stopped in early 

 stages, later stages not so much affected. 



2-24 cells ; normal ; no development while in boiled sea water. 



8-40 cells, normal ; no development while in boiled sea water. 



24-52 cells ; similar to preceding. 



No. 



879 



880 

 881 

 882 

 883 

 1,023 



1,024 

 1,025 



1,026 

 1,027 



1,028 



1,029 



Stage. 



1-40 cells. 



1-30 cells. 

 1-30 cells. 

 1-30 cells. 

 1-30 cells. 

 2-20 cells. 



2. Partial Atmosphere of Hydrogen. 



Hydrogen 

 Stream. 



3 hrs. 







2-20 cells 



4 J hrs, 

 Control. 



7* hrs 



Control 



2 hrs 



2-20 cells 



2-20 cells 



2 hrs 

 lhr. 

 lhr. 

 lhr. 

 lhr. 

 lhr. 



1-20 cells. 



H 60%— Air 40% 

 2-4 cells. 



H 70%— Air 30% 

 1-20 cells. 



H 70%— Air 30% 



Closed 

 Bottle. 



18 hrs. 



18 hrs. 



20 hrs 



12 hrs 



12 hrs 



24 hrs 



Open 

 Bottle. 



4J hrs, 



7J hrs 

 2 hrs. 



3 hrs 



3 hrs 



5 hrs 





Results. 



1-40 cells; nuclei of older stages normal; of earliei 



stages, large, achromatic, with large nucleoli. 

 1-30 cells; same as preceding. 

 4-48 cells, normal. 

 1-30 cells; same as No. 879. 

 24-52 cells, normal. 

 2-24 cells; nuclei and nucleoli large, chromatin clumped 



Fig 



polyasters; centrosomes and spindles 



2-24 cells; similar to preceding; centrosomes and 

 spindles unusually distinct 



cells; similar to preceding. Figs 



118. 



/elopment while in hydrogen ; after 20 hrs 



fresh sea water eggs had reached 48-86 cells. 



1-20 cells ; cleavage stopped ; nuclei nearly normal. 

 2-4 cells; cleavage stopped. 



1-20 cells ; similar to preceding 



Eggs from two experiments mounted together. 



3. Stoppered Bottles of Normal Sea Water. 



Results. 



4 cells to veliger; in early stages, division may be permanently halted 

 in metaphase and anaphase; framboisia; exogastrulse. 



Same as preceding. , ... -ummatin 



1-30 cells ; cleavage checked ; nuclei large and clear, witn cnrow» 



clumped, as in boiled sea water. 



