The Sexual Pliases of Myzostoma. 
235 
the course of later adventitious oocytes would be very difficult or 
impossible to trace between the closely packed ova with which the 
body-cavity is soon fìlled. 
The triplet-cells, though always recognizable as oocytes and 
accessory cells in the ovary, except in the very earliest stages, are 
most easily studied in the peripheral porti on of the organ just 
before or during their detachment. The series of changes which 
the ovum of M. cirriferum undergoes from the triplet-stage to maturity 
is represented in PI. 10 Figs. 6 — 15. Ali of these ova were drawn 
under the same power (Zeiss hom. im. oc. 3). Thej ova in 
Fig. 6ß — d were taken from a specimen killed in corrosive subli- 
mate, the remainder of the series from specimens killed in picro-acetic 
acid. The latter fluid is the better preservative for the chromatin 
at least during the early stages. 
An Ovum such as is readily found in the peripheral portion of 
the ovary or migrating through the body-cavity is shown in Fig. 6 a. 
Those in Fig. 6 h — d bave just attached themselves to the peritoneal 
•«pithelium. In ali these cases the nuclei of the accessory cells are 
xlistinctly visible at either end of the young oocytes, but there is 
-no longer any trace of a cell-limit between the cytoplasm of the 
accessory cells and that of the ovum. The cell-bodies of the three 
cells appear to fuse and form one ovai or elliptical trinucleate cell. 
.The deeply staining nucleolus in each nucleus remains distinct for 
some time; that of the ovum enlarges rapidiy. 
At first (Figs. 7, 9 and 10) the chromatic skeiu of the germinai 
vesicle, or oocyte-nucleus, is quite distinct and appears to form a 
-continuous filament of uniform thickness throughout (Fig. 7). Later 
this skein resolves itself into a series of caryomicrosomes (Figs. 9 
and 10). Finally (Fig. 8) the skein passes into the reticular stage 
leaving a more or less open space around the eccentric nucleolus. 
During these stages the accessory nuclei grow apace and their 
.boundaries become more difficult to trace. This is due in part to 
the fact that at the poles of the ovai trinuclear mass the nuclear 
«outlines reach the cell-boundary and appear to fuse with it, while 
in the opposite direction they reach the walls of the germinai vesicle. 
Hence there is only a limited region in which the membrane of the 
accessory nucleus may stili be detected (Fig. 8). 
As the ova grow the cytoplasm becomes denser and acquires a 
greater affinity for the haematoxylins and carmines. Eggs in this 
stage are shown in Figs. 11—14. In ali of these — excepting Fig. 14 
