1908] YAMANOUCHI— SPERMATOGENESIS AND OOGENESIS 157 



plate being laid down so as to divide the cytoplasm into two unequal 

 cells. The immense amount of food material in the ventral cell causes 

 its nucleus to grow more rapidly than that of the neck canal cell. At 

 this time these two nuclei contain 66 or 64 chromosomes. 



Then follows one more mitosis (simultaneous or successive) in 

 each of these cells. The mitosis which divides the neck canal cell into 

 two daughter cells is typical vegetative (figs. 43-45). In the telophase, 

 when the daughter nuclei are formed, a cell plate is laid down as 

 usual, but it soon begins to disorganize and finally disappears entirely. 

 The direction of this mitosis is various, being sometimes parallel to 

 the long axis of the archegonium, sometimes perpendicular to it, and 

 sometimes oblique. 



The ventral cell sooner or later divides into a ventral canal cell 

 and an egg cell (figs. 46-48). No peculiarity is observed in this 

 mitosis except in the metaphase (fig. 46), when there is almost always 

 present a single dark staining body near the spindle, which pos- 

 sibly may be a persistent nucleolus, but its origin was not traced. 

 The peculiar thread structure of unknown substance which is differ- 

 entiated in the central cell is also continuously observed in the ventral 

 cell, without any visible connection with the mitotic figure. In the 

 telophase, the two daughter nuclei show a marked difference in size 

 and shape, perhaps due to a nucleo-cytoplasmic relation, similar to 

 the case previously observed (fig. 47). Several nucleoli appear in the 

 young daughter nucleoli (fig. 48) . 



The characteristic curvature of the nucleus of the egg cell begins 

 at the telophase of this division, and there is laid down by this time a 

 dome-shaped cell plate which is of longer duration than that between 

 the neck canal cells. The egg nucleus grows to an immense size and is 

 very irregular in outline, whereas the neck canal cell and the ventral 

 canal cell collapse and become mucilaginous, together with their 

 disorganizing nuclei. 



FERTILIZATION 



The egg cell when ready for fertilization lies in the bottom of the 

 archegonial cavity. Some of the material resulting from the disor- 

 ganization of canal cells remains in the neck and ventral region of the 

 archegonium as a slimy substance, even after the wide opening of the 



