PLATE VII. 



Sections of Eggs of Cynthia partita; Fertilization and Early Cleavages. 



Fig. 88. Division of sperm aster ; crescent substance at periphery on posterior side. 



Fig. 89. Similar to preceding but showing egg nucleus. 



Figs. 90 and 91. Sections at right angles to first cleavage plane but oblique to egg axis, showing the 

 union of pronuclei; clear and yellow protoplasm and sperm amphiaster in posterior half 

 of egg. 



Fig. 92. Section in the plane of the first cleavage (future median plane) showing the union of the 

 germ nuclei, the clear protoplasm and crescent on the posterior side of the egg, and the 

 polar bodies above. 



Fig. 93. Early prophase of the first cleavage, in the plane of the spindle axis. 



Fig. 94 and 95. Two dispermic eggs; the first showing two sperm nuclei on the posterior side of the 

 egg with a single crescent ; the second, two sperm nuclei and one egg nucleus, with the 

 clear protoplasm and crescent about equally divided, by a tongue of yolk, between the 

 two sperm nuclei. 



Fig. 96. Section in the plane of the first cleavage and transverse to the spindle, showing a cross sec- 

 tion of the equatorial plate near the middle of the egg, surrounded by clear protoplasm, 

 also the crescent at the posterior border with some of the yellow spherules all around 

 the spindle. 



Fig. 97. Metaphase of the first cleavage; equatorial section at right angles to the preceding. 



Figs. 98 and 99. Early and late anaphases of the first cleavage; sections in equatorial plane. 



Fig. 99. Constriction of cell body; chromosomal vesicles at the ends of the nuclear spindle. In both 



figures the daughter centrosi is are elongating in the equatorial plane and at right 



angles to the first spindle axis. 



Fig. 100. Telophase of the first cleavage, showing the rotation of nuclei, eentrosomes and cytoplasm 

 toward the animal pole of the egg. 



Fig. 101. Equatorial section, prophase of second cleavage; crescent substance at the posterior pole. 



Fig. 102. Section at right angles to the preceding and through the axis of one of the spindles; nucleus 

 and cytoplasm lie above the equator, yolk and crescent below. 



Fig. 103. Equatorial section showing precocious division of the eentrosomes in one of the blastomeres. 



Fig. 104. Anaphase of second cleavage; equatorial section ; chromosomal vesicles at ends of nuclear 

 spindles. 



Fig. 105. Telophase of second cleavage ; equatorial section, showing the bending of the middle of the 

 spindle toward the center of the egg, and a large amount of clear cytoplasm aud of 

 crescent substance in the posterior quadrants. 



Figs. 106 and 107. Two sections through one and the same egg in the eight-cell stage ; the first 

 through the anterior blastomeres ; the second through the posterior. The cytoplasm is 

 most abundant in the cells at the animal pole, the crescent substance in the two posterior- 

 vegetal cells, though it is also found around all the nuclei. The polar bodies, which are 

 shown in stippled outlines, are not in the plane of either of these sections, but in the 

 region between them. 



