Part 7

82. Spermatid showing a conspicuous chromatin element in nucleus, and spindle-remains (s) elongated.

83. Spermatid, showing centrosome (c) and divided spindle-remains (s and a).

84. Older spermatid, showing centrosome (c), axial fiber of tail, and spindle-remains (s).

85. Spermatid, showing acrosome material (a) migrating to side of nucleus opposite centrosome.

86. Slightly older spermatid.

87. Later stage of spermatid, showing condensed chromatin, elongated centrosome (c), acrosome material (a), and spindle-remains (s).

88-89. Older spermatids, showing formation of acrosome (a) and middle piece (m).

90-92. More advanced stages.

93. Mature spermatozoön.

Blattella germanica.

FIG. 94. Somatic cell from egg follicle, 23 chromosomes.

95. Spermatogonium, showing chromatin element (x) associated with a nucleolus (n).

96. Same, prophase of mitosis.

97. Equatorial plate of spermatogonial mitosis, 23 chromatin elements.

98. Young spermatocyte, showing centrosome (c) and U-shaped element (x).

99. Young spermatocyte, element x attached to one end of a long, fine spireme.

100. Coarser spireme stage.

101-103. Bouquet stage.

104-105. Later spireme stage.

106. Various forms assumed by the combined nucleolus and element x; last figure from a giant cell.

107. Segmenting spireme.

108. Similar stage to fig. 107, one chromosome longitudinally split; element x present.

N. M. S. del.]

PLATE IV.

Blattella germanica.

FIG. 109. Similar stage to figs. 107 and 108; chromosomes U-shaped and not longitudinally split; two centrosomes present (c).

110. Longitudinally split chromosomes.

111-113. Various stages in formation of cross-shaped tetrads.