i9o8j YAMANOUCHI—SPOROGEN'ESIS IN NEPURODIUM 29 



Figs. 24a, 24^, 24c. Three sections of the same nucleus after segmentation 

 of spirem into 66 bivalent chromosomes; association of t^vo halves of each chro- 

 mosome has become somewhat loose, so that various combinations of the two 

 daughter halves are shown, such as H, I, J, K, L, 0, U, V, X, Y, and so forth; 

 thin strands of chromatin material visible attached to the ends of chromosome; 

 two chromosomes (a and h) are cut into two, so that the two parts of the each 

 chromosome appear in two successive sections- 



FiGS. 25a, 256, 25c. Four sections of the same nucleus; chromosomes show 

 spiny structure; nuclear membrane has disappeared, the outline of nuclens being 

 maintained by the encroaching and anastomosing of fibers; tvvo chromosomes 

 (a and h) are cut into two, so that the two parts of each chromosome appear in 

 two successive sections. 



PLATE III 



Sporogenesis continued 



Figs. 26a, 26b. Two sections of the same nucleus, after intrusion of fibers; 



multipolar spindle is established. 



Figs. 27a, 276. Two sections of the same nucleus, after the multipolar spindle 

 has passed into the bipolar condition; bivalent chromosomes, two daughter halves 



always in pairs, have shortened considerably. 



Fig. 2S. Early metaphase, the bivalent chromc^omes being regularly ar- 

 ranged in an equatorial plate. 



Fig. 29. Polar \iew of early m.etaphase; li^tly shaded chromosomes repre- 

 sent those which could be seen at a deeper focus; 64 bivalent chromc^omes are 



present. 



Metaphase; dau^ter chromosomes begin to separate 



that sho^-n in fig. 30; some of the dau^t 



for the second mitosis. 



pole indicate a new fission that 



Anaphase: rate of movement of daughter chromosomes 



pole is variable. 



Fig. 1,7,, Late anaphase; some of the daughter chromosomes at tl^ pole 

 still show V-shape, due to the fission first indicated in fig. jr. 



Fig. 34. Early telophase; daughter chromosomes are grouped at the pole, 

 two of them being tardy; no V-shaped chromosome present. 



Fig. 35. Polar \'iew of stage shown in fig. 34^ showing 64 chromosomes. 



Fig. 36. Telophase \iewed from the pole; chromosomes vacuolized; nuclear 



membrane constructed. 



Fig. 37. Polar view of daughter nucleus in a later stage of telophase; vacuo- 

 lization farther advanced. 



Fig. 38. Daughter nucleus begins to grow in size; mass^ of the chromatin 

 reticulum may represent main bodies of vacuolized chromosomes; graBukr 

 structure begins to arise along periphery of equatorial region where fibers from 

 pol^ meet- 



