The Spermato genesis of Aplopus inayeri. 35 



FIGS. 74, 75, 76, 77. Equatorial plates of first maturation mitosis, each with 18 chro- 

 mosomes; among these, the accessory can be recognized as the lari;. 

 U-shaped or irregularly oblong body. 



FIG. 78. Early anaphase of first maturation mitosis, showing very elongate daughter 

 chromosomes with indication of a longitudinal split. The accessory has 

 assumed a position in advance of the ordinary chromosomes near one 

 pole and appears double. 



FIGS. 79, 80, 81, 82, 83, 84. Spindles of primary spermatocyte mitoses with some of the 

 chromosomes at late metaphase and some at early anaphase. These fig- 

 ures show the various typical forms of the accessory chromosome always 

 in advance of the ordinary chromosomes ; also the various forms of the 

 latter in the heterotypic division. This is a reducing division separating 

 entire chromosomes. 



PLATE 4. 



FIGS. 85, 86, 87, 88. Anaphase stages in the first maturation mitosis. U-shaped acces- 

 sory chromosome attached to pole by single thread. In late anaphase 

 stages the accessory chromosome becomes longitudinally split ; the con- 

 summation of the split represents a separation at the bend of the U. 



FIGS. 89, 90, 91. Late telophase ; the mass of ordinary chromosomes has moved by 

 the side of and beyond the accessory. 



FIGS. 92, 93, 94, 95, 96. Successive stages in the late telophase of the first maturation 

 mitosis ; the accessory chromosome appears distinctly double and never 

 passes into a reticular phase with the ordinary chromosomes at this stage. 



FIG. 97. Resting-stage interpolated between first and second maturation mitoses ; acces- 

 sory chromosome double and closely applied to nuclear wall. 



FIG. 98. Early prophase of second maturation mitosis; accessory chromosome stijl 

 double. The narrow rim of cytoplasm contains several masses of elimi- 

 nated chromatin. 



FIGS. 99, loo. Later prophase of secondary spermatocyte division ; both cells have the 

 double accessory chromosome. 



FIGS. 101, 102. Daughter-cells of the heterotypic mitosis in prophase for the second 

 division. Only one of these cells contains an accessory; only half of the 

 secondary spermatocytes have an accessory chromosome. 



FIGS. 103, 104, 105. Three secondary spermatocytes in prophase of final maturation 

 division, all of which contain the accessory chromosome. The segments 

 of the pale-staining mossy spireme give indication of a longitudinal split. 

 Cytoplasm is very scant. 



FIGS. 106, 107, 108. Later stages in the prophase of the second maturation mitosis, of 

 which figure 107 contains an accessory chromosome (a). 



FIG. 109. Metaphase of second maturation division. 



FIG. no. Equatorial plate with 18 chromosomes. The large U-shaped chromosome 

 is the accessory. 



FIGS, in, 112. Equatorial plates with 17 chromosomes; the accessory lacking. 



PLATE 5. 



FIG. 114. Four contiguous cells (pairs of daughter-cells from two primary spermato- 

 cyte mother-cells) showing the chromosomes in the equatorial plate. The 

 number of chromosomes alternates from 18 to 17 among the four plates. 

 The first and third contain a large U-shaped odd chromosome, the accessory. 



FIGS. 113, 115. Early anaphases of second maturation mitosis, both showing the acces- 

 sory chromosome entering the spindle perpendicular to the mantle fibers. 



FIGS. 116, 117. Late anaphase and telophase, respectively, showing the lagging of the 

 division products of the accessory chromosome. 



FIG. 118. Late telophase; accessory chromosome projecting beyond the main mass 

 of ordinary chromosomes. 



FIG. 119. Various tetrad figures showing forms assumed by the ordinary chromosomes 

 in the prophase and early metaphase of the heterotypic mitosis. 



FIG. 120. Two spermatids, both with daughter accessory chromosomes ; the ordinary 

 chromosomes are in the irregular, granular, lightly-staining condition of 

 the late telophase. The cell to the left shows the mid-body at its lower 

 pole. 



FIG. 121. Three spermatids, two with accessory chromosome. Only one-half of the 

 spermatids can have an accessory. 



