140 BULLETIN OF THE 



the number of nuclei in each cell, and he found no evidence of division 

 among them. The outline of the nuclei, which measure about 15 ^ in 

 diametei', is frequently somewhat irregular or lobed. Like the nuclei of 

 the serosa, they are flattened tangeutially (Fig. 2, nl. am.) ; but not- 

 withstanding this, they cause an outward bulging of the cell upon the 

 serosa, as shown in Figure 2. They contain always one or more highly 

 refractive, deeply staining nucleoli. The rest of the scanty chromatic 

 substance is in the form of minute granules, occasionally arranged partly 

 in a very faint network (Fig. 18, 6 and c). As in the nuclei of the 

 serosa, chromatic threads frequently unite the nucleoli. 



Division of the amniotic nuclei is of rare occurrence. In only one of 

 my preparations are dividing nuclei at all abundant. The division 

 takes place without mitosis, but is of a different type from that of the 

 nuclei of the serosa. The only alteration of the chromatin is possibly 

 a change in the position of the nucleoli ; I have not been able to detect 

 any modification of the reticulum. The first sign of approaching divis- 

 ion is elongation of the nucleus (Figs. 16 and 18, a). A deep narrow 

 constriction appears at the equator of the nucleus (Fig. 17). This is 

 followed by the formation of an equatorial septum, at once partition- 

 ing off the nucleus into two daughter nuclei (Fig. 18, b). If there are 

 but two nucleoli, it is the rule to find one in each daughter nucleus ; but 

 where there are several, they are often unequally apportioned. After 

 the formation of the septum, the daughter nuclei still adhere to each 

 other, and division seems always to be attained by deepening of the 

 equatorial constriction in the plane of the septum (Figs. 18, b, c, and 19). 

 I have not found any evidence of a recession of the nuclei before 

 division of the cell. Furthermore, the rarity of binucleate cells makes 

 it very probable that cell division follows nuclear division promptly. 

 As in the serosa, division of the cell takes place by the formation of a 

 cell wall without marked constriction (Fig 20). The position of the 

 nuclei in this figure, and the frequency with which nuclei are found 

 near the boundaries of the cells (Fig. 1, am.) is evidence of the prompt- 

 ness of cell division after the division of the nucleus. 



It is clear that Chun's hypothesis will not hold in this case, for there 

 is even less tendency than in the serosa to accumulate nuclei in the 

 cell. This may be owing in part to the shai)e of the cell, for it is sel- 

 dom elongated. It would seem that, in case the cell becomes elongated, 

 nuclear division takes place and the cell divides immediately after the 

 nucleus. The orientation of the nuclei with reference to the cytoplasm 

 of their respective cells would then be accomplished by their migration 

 to the centre of the cells. 



