Explanation of Plate VII. 



Fig. 1. Pole view of spermatogonial ruetaphase, showing the thirty-three chro- 

 mosomes. It will be observed that the chromosomes are of unequal sizes, and 

 that the large ones arrange themselves in a circle on the outside of the figure. 



Fig. 2. Very young spermatocyte. The chromatin derived from the break- 

 ing down of the spermatogonial chromosomes in a diffuse condition, with no trace 

 of a linear arrangement. The accessory chromosome x on the periphery of the 

 nucleus, darkly staining and homogeneous. 



Fig. 3. Early stage in the formation of the spireme. In the cytoplasm the 

 remains of the spermatogonial spindle. The cell has entered upon the growth 

 period. 



Fig. 4. A later stage in the spireme formation. The accessory chromosome 

 larger and more flattened. A surface view shows it as an apparently fenestrated 

 plate. The remains of the two spermatogonial spindles still persisting. 



Fig. 5. First appearance of definite chromosomes. One shown entire with 

 longitudinal and cross-divisions marked. The accessory chromosome is here seen 

 to be in a spireme condition. 



Fig. 6. Condition of the chromosomes after further contraction of the early 

 segments. As here shown, they are more granular than is usually the case. 



Fig. 7. Common types of the prophase chromosomes. 



Fig. 8. A cell in which one of the chromosomes has its halves widely sepa- 

 rated along the longitudinal division, forming Paulmier's double-V figure. 



Fig. 9. In this cell may be seen the variation in form and size of the early 

 spermatocyte chromosomes. 



Fig. 10. Two cells of the late prophase, with the chromosomes at almost the 

 extreme degree of concentration. 



Fig. 11. Chromosomes of cells in the stage shown in figure 10. These repre- 

 sent the different types of rings, crosses, etc., commonly observed in first sper- 

 matocytes just before the formation of the mitotic figure. 



Fig. 12. Different forms assumed by the accessory chromosome in the pro- 

 phase of the first spermatocytes of Xiphidium. 



Fig. 13. Metaphase of the first spermatocyte. The accessory chromosome is 

 seen at one pole of the spindle, to which it has moved before the separation of 

 the chromatids of the remaining chromosomes. 



Fig. 11. Another cell in about the same stage as that represented in the pre- 

 ceding figure. 



Fig. 15. A first spermatocyte metaphase in which the accessory chromosome 

 has not as yet moved to the pole of the spindle. This is uncommon in OrcJn s- 

 tieus, but frequent in Anabrus. 



Fig. 1G. Pole view of a first spermatocyte metaphase, showing seventeen chro- 

 mosomes. The variation in size of the elements, so marked in the spermatogonia, 

 is even more pronounced here. This is a cell similar to that of figure 15, in which 

 the accessory chromosome lies in the equatorial plate. 



