22 DESCRIPTION OF PLATES. 



Plate II. 



Stenopehnatus. 



Figs. 46-47. Nuclei of spermatogonia, showing 2 and 3 nucleoli (m). 



48-49. Prophase of spermatogonial mitosis, showing two exceptionally large 

 chromosomes of equal length. 

 SO. Equatorial plate of spermatogonial mitosis, 46 chromosomes. 

 51-54. Spermatocytes in spireme stage, nucleus containing a nucleolus (m), 

 and a chromatin element {x), which is attached to one end of 

 spireme and gradually increases in size during growth stage of 

 spermatocytes. 



55. Spireme longitudinally split and showing the beginning of cross for- 



mation. 



56. Spireme segmented, tetrads forming. 



57. One split segment and a part of another connected by bands of linin. 



58. More open cross and diamond forms ; element x conspicuous. 



59-60. More contracted cross and diamond-shaped tetrads ; linin bands shown 



in 60, where element x is also present. 

 61. Different forms assumed by element x during tetrad stage (figs. 56-60) 

 62-63. Diamond-shaped and contracted cross-shaped tetrads from metaphase 



of first maturation mitosis, showing linin connections. 



64. Diamond-shaped tetrad with spindle-fibers attached ; a-a, probably 



halves of one univalent chromosome ; b-b, halves of the other. 



65. Dyad from anaphase of first maturation mitosis. 



66-67. Metaphase of first maturation spindle, showing element x in different 

 positions. 

 68. Late anaphase of same. 

 69-70. Equatorial plate of first maturation spindle, 23 chromosomes and ele- 

 ment X below, in fig. 69. 

 71. Chromatin massed at poles of spindle ; element x isolated at one pole. 

 72-72- Two resting spermatocytes of the second order, one containing ele- 

 ment X, the other not. 

 74-76. Successive stages of breaking down of element x. 



77. Prophase of second division ; dyads evident, but no sign of x in this 



or following stages. 



78. Second spermatocyte division — metakinesis. ' 



79. Same ; late anaphase. 



