22 DESCRIPTION OF PLATES. 



Plate II. 



Stenopelmatus. 



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



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

 chromosomes of equal length. 

 50. Equatorial plate of spermatogonia! mitosis, 46 chromosomes. 

 51-54. Spermatoc34es in spireme stage, nucleus containing a nucleolus (n), 

 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 .*■ isolated at one pole. 

 72-73. 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. 



