SUTTON : SPERMAT(JGONIAL DIVISIONS IN BRACHYSTOLA MAGNA. 159 



Fig. 28. Cross-section of spindle, showing nearly all the fibers arranged in an 

 outer cylinder, a verj- few being irregularly disposed within. 



Fig. 29. Telophases, showing sixteen chromosomes in each daughter-cell. 



Fu.. 30. Later telophase. Membranes formed and already fused, producing a 



single sacculated or glove-shaped nucleus. Apparent longitudinal split of 

 chromosomes due to the fact that they are hollow. 



Fig. 31. Two daughter-cells, showing incomplete separation in halves of the ac- 

 cessory chromosome. The partition wall has constricted across and is cut- 

 ting off one of the accessory chromosomes which has already entered upon 

 the vesicular stage. A thickening of the free margin of the partition wall 

 may be seen where it presses upon the connecting element. The cells have 

 rolled upon one another so that they are now side by side instead of end to 

 end. 



Fici. 32. Slightly later telophase, showing chromosomes and membranes in cross- 

 section. Some of the sacculations of the nucleus appear to have fused 

 throughout their length. 



Fig. .33. Telophase of last generation of secondary spermatogonium, showing 

 vesicular chromosome on right and almost complete loss of partitions be- 

 tween the pockets of the nuclear cavity. 



Fig. .34. Cell in. similar stage, showing vesicular chromosome in cross-section. 

 The apparent longitudinal split of chromosomes is due to the hollow space in 

 the middle of each. Cross-hatched body below nucleus is to represent 

 spindle remains, which in this case had become homogeneous and apparently 

 stained only with the osmic acid. 



Fig. 35. Fragment of cell, showing entire vesicular chromosome. 



Fig. 36. Late telophase of last generation of spermatogonia. Accessory chromo- 

 some is of about the same density as the others, and is closely applied to the 

 nuclear membrane. Spaces between pockets of nucleus are reduced to mere 

 furrows in the nuclear wall. Chromosomes have begun to lose their former 

 sharp outlines. 



Fig. 37. Later stage. Accessory chromosome has become more condensed. 

 Nuclear membrane is smoother and the outlines of the chromosomes are 

 entirely lost. 



Fig. 38. Early spermatocyte, spireme forming. Both nucleus and cell body 

 have increased greatly in size. Accessory chromosome, closely invested by 

 its membrane, lies partly imbedded in the nuclear wall. The former is di- 

 vided in the section and in its center may be seen the persisting cavity of the 

 vesicular stage. Cross-hatched bodies above the accessory chromosome are 

 spindle remains, similar to those described for fig. .34. 



Fig. 39. This figure represents a stage of development between figs. 19 and 20. 

 The condition of the chromosomes as almost straight double rods is unusual. 

 At the side of the cell opposite to that occupied by the centrosome in the 

 previous division may be seen the centrosomes of the next, each with its 

 aster, and the two separated by a minute centrodesmus. The accessory 

 chromosome does not appear. 



Fig. -10. Degenerating primary spermatogonium', from center of young cyst. 



Fig. 41. Section through upper portion of resting primary spermatogonium 

 which has assumed the function of a cvst cell. 



