586 CELL DIVISION IN EGGS OF CREPIDULA. 



Fig. 77. Exp. 919: Egg subjected to pressure, probably after formation of 1st set of micromeres. 

 In quadrant B and D the 2d set of "micromeres" are really macromeres. 



Fig. 78. Exp. 1110 (2): 5 mil. amp., 2 min., normal 22 hrs. Egg with scattered blastomeres in the 

 stage of the formation of the 2d set of micromeres. 



Fig. 79. Exp. 1121 (3): 5 mil. amp., 10 min., normal 16 hrs. Egg in stage of formation of 2d set of 

 micromeres, showing effects of pressure. 



PLATE XLIX. 

 Effects of Electric Current. 



Fig. 80. _ Exp. 997 (3) : 1 volt, 15 min., normal 30 min. Egg and sperm nuclei are large and contain 

 little chromatin, sphere material in granules, no segregation of yolk and cytoplasm. 



Fig. 81. Exp. 997 (3): Similar to preceding. 



Fig. 82. Exp. 1106: 5 mil. amp., 5 min., normal 17 hrs.; nuclear membrane dissolved and chromatin 

 clumped; development stopped. 



Fig. 83. Exp. 1106: Similar to preceding. 



Fig. 84. Exp. 1106: Similar to preceding. 



Fig. 85. Exp. 997 (3) : Similar to fig. 80, but with nuclear membrane gone. 



Fig. 86. Exp. 1140 (1): 2 mil. amp., 2 min., normal 5 J hrs. Chromatin disappearing. 



Fig. 87. Exp. 1140 (2): 5 mil. amp., 10 min. Ordinary tetraster. 



Fig. 88. Exp. 997 (2) : 1 volt, 15 min., normal 2 J hrs. Plasma and nuclei displaced by convection 

 current, as in centrifuged eggs. 



Fig. 89. Exp. 997 (2): Similar to preceding. 



Fig. 90. Exp. 1121 (2): Chromosomes have disappeared leaving the spindle fibers a little more 

 chromatic than in normal eggs. 



Fig. 91. Exp. 997 (2): 1 volt, 15 min., normal 2i hrs. Chromatin largely dissolved and displaced 

 toward lower pole; in right cell long strands of cytoplasm. 



Fig. 92. Exp. 1121 (2): 5 mil. amp., 10 min., normal 3 i hrs. Spindle and chromosomes disappearing 

 in left cell; others normal. 



Fig. 93. Exp. 998 (2): 4 dry cells If hrs., normal 11 hrs. Evidently egg was in an advanced stage 

 (ca. 42 cells) at the time of the experiment. Although the cells are not dead, the micromeres are rounded 

 (framboisia) and many have dropped off. 



PLATE L. 



Effects of Abnormal Temperature. 



Fig. 94. Exp. 1170 (1): Ca. 38° C. 1 hr.; egg irregular in outline, with archiplasm withdrawn into 

 amphiaster, and into the surface layer. First maturation amphiaster irregular in shape and chromosomes 

 scattered; sperm nucleus near vegetal pole. 



Fig. 95. Exp. 1174(2): 37° C. i hr., room temp. (27°) 3 hrs.; first polar body very large; chromosomes 

 of second maturation division have formed karyomeres; sperm nucleus near animal pole. 



Fig. 96. Exp. 1171 (1) :_ Ca. 35° C. § hr.; 2-cell stage, showing dense aggregation of archiplasm 

 around nuclei and spheres, with different lands of cytoplasm in other parts of cell. 



Fig. 97. Exp. 1171 (1): Similar to preceding; second cleavage spindles greatly modified; chromosomes 

 scattered; archiplasm gathered in spindle areas and division wall. 



Fig. 98. Exp. 1171 (2): Ca. 35° C. J hr., room temp. (ca. 24°-26°) 15 hrs.; the archiplasm has col- 

 lected in central areas in each cell and in division walls; chromosomes are clumped and thrown out of cyto- 

 plasmic areas. 



Fig. 99. Exp. 1171 (2): Similar to preceding. 



Fig. 100. Exp. 962: On ice 16 hrs.; the spheres of the third cleavage are unusually distinct and the 

 scattered sphere granules of the second cleavage (in the micromeres) are very large. 



Fig. 101. Exp. 962: The spheres have a definite boundary, stain more deeply than usual and look 

 almost like nuclei. 



Fig. 102. Exp. 962: A later stage, with spheres similar to those shown in fig. 101. 



Fig. 103. Exp. 964: On ice 40 hrs.; the sphere granules are especially large. 



Fig. 104. Exp. 964: Similar to preceding. 



Fig. 105. Exp. 964: Similar to preceding; many of the sphere granules are vesicular. 



PLATE LI. 



Effects of Decreased Oxygen Tension. 



Figs. 106-109. 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 y. 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. 



