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On the ovogenesis and spermatogenesis of Sagitta bipunctata. 233 
egg-membrane is closely applied on all sides to the surface of the 
two accessory cells, as on the right-hand side of the figure; in others, 
one or more epithelial cells are connected with the micropyle open- 
ing, as on the left-hand side of the figure; and very often an opening 
is seen between the cells and the membrane, as though the egg were 
on the point of breaking away between the two accessory cells. 
CLAPAREDE (1863) described the oocytes of Sagitta as having a 
pedicel composed of 5 or 6 cubical cells, and Grassı (1883) describes 
and figures a pedicel consisting of a single cell which, he says, in nearly 
ripe ova becomes amorphous and in some preparations seems to be 
perforated ; but neither of these authors associated these cells with the 
process of fertilization, and I know of no other such case in the 
literature. To determine what happens between the stages shown in 
Figs. 2a, and 16, and the giving off of the polar bodies, as de- 
scribed by Bovert (1890), it only remains to kill the animals at the 
moment when the laying of the eggs begins, and study sections 
of the ripe oocytes remaining in the ovary. This I hope to do at 
some future time. 
‘I have examined my sections very closely for an opening from 
the ovary into the oviduct, but find none. The indications are, how- 
ever, that such an opening must be formed at the posterior larger 
end of the sperm-oviduct when the eggs are laid; and that the ova, 
already containing the sperm nuclei, break away from the outer ac- 
cessory cells, and pass posteriorly through such an opening, and 
thence out into the water. If such is the case, as HERTWIG thinks 
probable (1880), only the posterior end of the duct is properly an 
oviduct, and the whole anterior portion, extending the entire length 
of the ovary, is simply a spermduct through which the spermatozoa 
reach the ripe oocytes, entering through the openings and tubes pre- 
pared for them by the accessory cells. 
The points of special interest in the ovogenesis of Sagitta are: 
1) the unbroken continuity of the reduced number of chromosomes 
during the whole growth period of the oocytes; 2) the increase in 
_ length and the branching of the chromosomes, as the oocytes increase 
in size, and the very great reduction in the size of the chromosomes 
as the oocytes ripen; 3) the casting out from the nucleus of a large 
number of what appear to be chromatin granules, at about the time 
when the spermatozoon enters the accessory cells; 4) the connection 
of each oocyte with two accessory cells, within which is developed a 
definite path for the spermatozoon from the spermduct to the ovum. 
