130 BULLETIN OF THE 
for the most part in the form of granules distributed evenly throughout 
the nucleus. Indications of a reticular or filamentous structure are, 
however, frequently present. I believe there is a chromatic network 
throughout the nucleus, but the abundance of granular chromatin pre- 
vents one from tracing it. Several nucleoli are always present. They 
are extremely variable in size and shape, and in many cases appear to 
be only aggregations of granular chromatin. They take a stain with 
hematoxylin and carmine in no way different from the rest of the 
chromatin, except that it is more intense. 
A very large proportion (about four to one) of the cells of the serosa 
contain two nuclei. These pairs of nuclei have all arisen from single 
nuclei by amitotic division. It is obvious that division of the cell is not 
contemporaneous with, aud does not immediately follow, the division of 
the nucleus. In many cases, especially when the embryo is far ad- 
vanced, cell division probably does not occur at all. Very few cells out 
of the thousands I have examined have had more than two nuclei; but 
I have found several with three nuclei, and two cells with four. ‘This 
seems to be the maximum number. These cells of the serosa, therefore, 
are not to be classed with multinucleate cells in which the nucleus 
divides into a great number of irregular and unequal fragments. Here 
the division takes place in an orderly fashion, and division of the cell 
follows nuclear division in regular sequence, though not immediately. 
In every serosa examined, nuclei were found in process of division. 
Some preparations furnish many more examples of-division than others ; 
and occasionally three or four adjacent cells will contain dividing nuclei 
(Fig. 15). Very frequently, however, only one or two dividing nuclei 
will be found in the whole serosa. It cannot therefore be supposed that 
nuclear division is frequent; and I have found that there are more cells 
with dividing nuclei in the membranes of late stages of the embryo 
than in the earlier ones. 
The first sign of approaching division is an elongation of the nucleus 
(Fig. 4), almost always parallel to the long axis of the cell. Naturally, 
the clongation progresses by insensible gradations from the nearly circu- 
lar form of the resting nucleus, so that one cannot say positively that 
the nucleus is going to divide until the elongation has become marked. 
The absolute amount of elongation varies greatly, and is less in the 
membranes of young embryos than in those of older ones. The example 
represented in Figure 4 is from an old membrane, and shows almost the 
extreme of elongation. This stage, while giving not the slightest evi- 
dence of ordinary mitosis, is characterized by a longitudinal arrange- 
