586 CELL DIVISION IN EGGS OF CREPIDULA. 



Fig. 77. 

 quadrant 



micromeres" are really macromeres. 



micromeres 



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



'& 



micromeres 



Fig. 79. Exp. 1121 (3): 5 mil. amp., 10 min., normal 



formation 



micromeres, showi 



PLATE XLIX. 



Effects of Electric Current. 



Fig. 80. 



normal 30 min 



sperm 



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



and cyt 



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



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 h\ 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\ 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 2 \ 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| hrs. Spindle and chromosomes disappearing 



normal 

 Fig. 93. Exp. 998 (2): 4 dry cells If hrs., normal 11 hrs 



was 



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



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 Exp. 1170 (1): Ca. 38° C. 1 hr.; egg irregular in outline, with archiplasm withdrawn into 



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



amphiaster, anc 



scattered ; sperm nucleus near vegetal pole. 



Fig. 95. Exp. 1174 (2) : 37° C. \ 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 kinds 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. h 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 oi cyto- 

 plasmic areas. 



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



100 



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



granules of the second cleavage (m the micromeres 



almost 



Fig. 101. Exp. 962: The spheres have a definite boundary 



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



Fig. 103. Exp 



granules are especially 



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



Fig. 105. Exp. 964: Similar to preceding; many of the sphere granule 



PLATE LI. 



Effects of Decreased Oxygen Tension. 



Figs. 106-109. Exp. 1010: Eggs placed for 36 hrs. in sea water which had been boi led, to *J^. 

 contained gases, and then cooled ; all development was completely stopped, but eggs were noWj ^ 

 tin in the resting nuclei is collected into one or more masses; spindle fibres are distinct but ast m j^ 

 lacking; centrosomes and sphere granules are vesicular. The eggs used in this expenmen 

 smaller than normal, being only 120 m in diameter. *i«.nii<rh which 



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

 hydrogen had been run for 1 hr.: development completely stopped: nuclei and nucleoli large, an 



