PLATE LI. 



Effects of Decreased Oxygen Tension. 



Figs. 105-109. Exp. 1010: Eggs placed for 36 hrs. in sea water which had been boiled to drive off 

 contained gases, and then cooled; all development was completely stopped, but eggs were not killed; chroma- 

 tin in the resting nuclei is collected into one or more masses ; spindle fibres are distinct but astral rays are 



lacking; centrosomes and sphere granules are vesicular. The eggs used in this experiment were much 

 smaller than normal, being only 120 n in diameter. 



Figs. 110-111. Exp. 1025: Eggs left for 18 hrs. in a stoppered bottle of sea water, through which 

 hydrogen had been run for 1 hr.; development completely stopped; nuclei and nucleoli large, little chromatin. 



Fig. 112. Exp. 1016: Eggs placed for 27 hrs. in sea water which had been boiled and cooled; similar 

 to preceding, development stopped. 



Fig. 113. Exp. 1017: Eggs left for 48 hrs. in stoppered test tube of boiled and cooled sea water; 



development completely stopped ; sphere granules prominent. 



Fig. 114. Exp. 1016: Same as fig. 112; nuclei with little chromatin; sphere granules prominent. 



Fig. 115. Exp. 1023: Eggs subjected to atmosphere of hydrogen for 2 hrs. and then left in open bottle 

 for 2 hrs.; development stopped; eggs similar to all others subjected to decreased oxygen tension. 



Fig. 116. Exp. 1017: Same as in fig. 113: The spindles are small, deep-staining and without astral 

 rays ; the chromosomes are arranged in a ring around the spindles. 



Figs. 117-118. Exp. 1025 : Eggs left for 18 hrs. in stoppered bottle of sea water through which hydrogen 

 had been run for 1 hr.; eggs similar to fig. 115; in fig. 118 there is an area of yolk (F) around the upper 

 poles of the spindles. 





