_Stenopelmatus._

FIG. 80. Telophase of second maturation mitosis.

81. Young spermatid, showing spindle-remains at _s_.

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 spermatozoon.

_Blattella germanica._

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

95. Spermatogonium, showing chromatin element (_x_) a.s.sociated 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. Coa.r.s.er spireme stage.

101-103. Bouquet stage.

104-105. Later spireme stage.

106. Various forms a.s.sumed 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.

[Ill.u.s.tration: STEVENS. PLATE III.

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.

114-117. Bent rods, U-shapes, split rings, pairs of rods, and rod-shaped tetrads (116), which are equivalent to the crosses of figs. 112-113.

118-122. Metaphase of first maturation division, showing the element _x_ in various positions.

123-127. First maturation spindle in metaphase.

128. Same in anaphase.

129-132. Late anaphase, showing element _x_ double in 129, and a lagging tetrad in 130.

133. Telophase, with the element _x_ in one daughter cell.

134-136. Prophase of second maturation mitosis, showing dyads and element _x_.

[Ill.u.s.tration: STEVENS. PLATE IV.

N. M. S. del.

BLATTELLA GERMANICA.]

PLATE V.

_Blattella germanica._

FIGS. 137-141. Dyads contracting for second maturation mitosis.

142. Equatorial plate of second maturation spindle, containing 11 chromosomes.

143-144. Same, with 11 chromosomes and the element _x_.