No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 
in the size of the mitoses hardly afford a satisfactory criterion 
for deciding this point (Figs. 255-261). All the typical stages 
of the prophase and metaphase are to be found, though only in 
the arrangement of the chromatin, for I have been unable to 
find either centrosomes or achromatic spindle. After careful 
study of a large number of these dividing nuclei I find the 
nucleolus to persist in the nucleus throughout the mitosis. 
Further, it appears to retain its original size throughout this 
process, without any diminution in volume. Thus the nucleolus 
seems to be retained without change in the spirem and aster 
stages of the prophasis. In the dyaster stage (Fig. 258) each 
pole of the nucleus usually contains a nucleolus, so that the 
nucleus contains two nucleoli ; and when the nuclear divi¬ 
sion is completed, i.e . 9 when in one and the same cell two 
nuclei occur in close contact with each other, in the aster as 
well as in the spirem of the metaphasis, each daughter-nucleus 
has its own nucleolus (Fig. 257). Now the ovogonium contains 
only one nucleolus, so that we must assume either (1) that a 
division of the nucleolus has taken place during the mitosis, or 
(2) that to one of the daughter-nuclei is allotted the whole 
original nucleolus, while in the other nucleus a new one is pro¬ 
duced. I have not seen any dividing nucleoli in these mitoses, 
their small size being a great obstacle to their study. But I 
should judge that such a division occurs, for these reasons : 
(1) the nucleus of one or of both the daughter-nuclei has 
sometimes a somewhat elongate form (Fig. 257); and (2) in 
later stages of the ovum proper I have found dividing nucleoli, 
and these cases would show that if such divisions take place in 
stages subsequent to the mitosis they might also occur during 
the mitosis. The two cases of division of the nucleolus found 
are here figured (Figs. 264 and 265), and in each of the elongate 
nuclei is a dumbbell-shaped nucleolus lying in the longitudinal 
axis of the nucleus ; in these figures the two halves of each 
nucleolus appear unequal in dimensions, but this is so because 
neither of these nucleoli happened to lie wholly in the plane of 
the section. I have found numerous other cases of elongated 
nuclei, each with an elongate nucleolus without any median 
constriction (Fig. 270). These facts would show that a division 
