Blackman. — Spermatogenesis of Scolopeudra. 



PLATE 5. 



All .figures except 58, 67, mid 71, are magnified 900 diameters. 



Figures 56-70 show the conditions in the primary spermatocytes of the small type. 

 Fig. 50. " Vesicle " stage. In general appearance the cell is similar to those of 



the large type except in size. 

 Fig. 57. Early prophase, showing early stages in tetrad formation. The areho- 



plasm has collected at one side of the cell around the two centrosomes. 

 Fig. 58. Later stages in tetrad formation. The accessory chromosome is now 



plainly seen. X 960. 

 Fig. 59. Still later prophase. The chromosomes are becoming condensed. The 



centrosomes have approached the nuclear membrane and begun to 



separate from each other. Astral rays have arisen at the expense of 



the archoplasmic mass. 

 Fig. 60. Various stages and forms of tetrads ; a, b, c, early, mid, and late prophase, 



respectively. 

 Fig. 61. Prophase, later than that shown in Figure 59. The centrosomes have 



separated still further, moving along the nuclear memhrane. All of 



the archoplasmic mass has been converted into astral rays. 

 Figs. 62, 63. Late prophase. The nuclear membrane has disintegrated and the 



spindle is forming. In Figure 63 evidences of the formation of the 



mantle fibres from the linin network are seen. 

 Fig. 64. Still later stage, showing the extreme shortness of the spindle as first 



formed. 

 Fig. 65. Metaphase. The centrosomes and centrosphere are cone-shaped. The 



astral fibres are branched and also cross one another in the equa- 

 torial region. 

 Fig. 66. Late metaphase, showing the modified spindle. Some of the chromo- 

 somes have already divided. 

 Fig. 67. Anaphase. All of the chromosomes with the exception of the accessory 



one have divided and are passing toward the poles. This special 



chromosome is moving toward one pole undivided. X 960. 

 Figs. 68, 69. Telophase. The chromosomes are massed near their respective poles, 



and the individual elements are indistinguishable from one another. 



In Figure 69 the constriction of the cell wall has begun. 

 Fig. 70. Late telophase. 



Figures 71-76 represent stages of the secondary spermatocyte of the synall type. 

 Fig. 71. Prophase of the second spermatocyte. This often follows the telophase 



of the first spermatocyte without a reconstruction of the nucleus. 



The centrosomes migrate apart along the inner surface of the cell 



membrane as in the large spermatocytes. X 960. 

 Fig. 72. Metaphase. 



Figs. 73, 74. Early and late telophase, respectively, of second spermatocyte. 

 Figs. 75, 76. Spermatids of the small type. 



