i 9 o8] YAMANOUCHI— SPERMATOGENESIS AND OOGENESIS 151 



of chromosomes either remain in contact side by side throughout 

 their length, or diverge in the middle part, remaining attached only 

 at the ends; but the latter case is of short duration and soon they 

 become reunited in pairs. The chromosomes now shorten and assume 

 an L-shape, and there is established an early condition of an equatorial 

 plate in which the vertical arms of the L-shaped chromosomes are 

 parallel and directed toward the pole, while the horizontal arms lie in 

 the equatorial plane; the spindle threads are attached at the ends 

 directed toward the periphery of the equator (fig. 4). A polar view 

 in this stage shows that the horizontal arms hold almost a radial 

 arrangement, while the vertical arms are visible only in the optical 

 section of their ends (fig. 5). The shortening and thickening of the 

 chromosomes advance farther until they become short, rod-shaped, 

 and arranged in the equatorial plate. 



The separation of daughter chromosomes begins at once (fig. 6). 

 As a rule, it takes place similarly in each chromosome, so that the 

 daughter chromosomes proceed toward the pole as a set (fig. 7). 

 When the set of daughter chromosomes has reached the pole, they 

 remain for a short time as regularly arranged and straight chromo- 

 somes (fig. 8), the polar view of which clearly shows that the number 

 of the chromosomes is 66 or 64 (fig. p). The daughter chromosomes 

 grouped at the pole become drawn together tightly and vacuolization 

 begins. When the nuclear membrane is formed, the chromatin struc- 

 ture of the daughter nucleus shows polarity (fig. 10). The formation 

 of the cell plate is like that described for the vegetative mitosis of the 

 sporophyte. 



SPERMATOGENESIS 



A detailed description of the mitoses which take place from the 

 cutting-off of an antheridium initial from a superficial cell until the 

 formation of a spermatid mother cell will be omitted. The number 

 of chromosomes is always 66 or 64. The only point which seems 

 noteworthy is that in the central or primary spermatogenous cell there 

 were observed in the majority of cases threadlike structures imbedded 

 in the cytoplasm, sometimes very densely crowded together near the 

 cell wall. The length of these threads was various, and they were a 

 little more slender than the spirem that is usually present in the 

 mitoses of spermatogenous cells. No such structure was ever observed 



