THE AMERICAN LOBSTER. 
153 
of eggs of fairly uniform size. The stromaof germogenal tissue is reduced to a minimum, 
and there is no trace of the ovarian glands which subsequently appear (tig. 141). 
The anatomy of the ovary and the slow growth of the ovarian egg, which we have 
followed from the time the new eggs were laid during a period of two years, when the 
next batch are ready for extrusion, proves conclusively, as I have pointed out in 
earlier papers (93 and .97), that the breeding season of the lobster is not an annual 
one, as had been supposed. (See pp. 70-73.) 
We have seen in the foregoing account that the massive yolk of the eggs is 
produced in three ways : (1) It is manufactured in the protoplasm of the growing ovum 
from materials absorbed from the blood — the most fruitful source; (2) it is produced 
by the activity of the ovarian glands; (3) by the direct absorption of follicular cells. 
The fact that parts of the follicular epithelium become differentiated into glands 
at a definite period, and that these later become totally obliterated is certainly remark- 
able, but I do not see how the phenomena which have been described can receive any 
other interpretation. The yolk in Peripatus novce-zealandice is described by Lilian 
Sheldon (ISO) as arising in part from follicle cells. The latter pass into the egg 
through the tubular stalk by which this is attached to the ovary, and become converted 
into yolk. Yolk is said to originate also in the protoplasm of the ovum, as is commonly 
observed in Arthropods; also from the breaking up of a part of the germinal vesicle, 
and finally it is produced by certain parts of the ovarian tube itself. The condition 
usually found in Platyhelminthes, where there is a permanent yolk secreting gland, 
may thus be compared with that of Peripatus and the lobster, where this function is in 
some measure performed by parts of the follicular epithelium. 
THE ORIGIN OP THE OVA. 
The ova arise from nuclei of the germinal epithelium, as I have described in detail 
in a former work (94). The origin of the primary egg membrane from the follicular 
cells (tig. 148, plate 40) is well known, but it should be remembered that this chitin-like 
envelope is not completed until after the decay of the ovarian glands. Thus, in the 
eggs shown in fig. 142, plate 39, and fig. 149, plate 40, there is no membranous boundary 
between the yolk and glandular cells. . 
Oases of the apparent fusion of young ova, mentioned by Bumpus (30), are occa- 
sionally met with, but it seems to me probable that no real fusion ever occurs — the 
impingement of cell upon cell often seeming, however, to support this idea. 
THE METAMORPHOSIS OF THE GERMINAL VESICLE. 
The very young ovum has a large, rapidly growing germinal vesicle or nucleus, 
as shown in fig. 154. At this stage the cell protoplasm forms a thin peripheral zone 
having a fine granular appearance in stained sections. 
The metamorphosis of the germinal vesicle from this early stage to the perfectly 
ripe condition is illustrated by figs. 155 to 1G1, all of which are drawn to the same 
scale. The nucleolus is formed at a very early period (fig. 154) and is soon vesiculated 
(fig. 155). Barely two or more nucleoli are present (fig. 156) ; there is usually but one. 
The nucleus reaches its largest size (about -p, mm. in diameter) at the close of 
the first year after ovulation. It is now regularly oval, its long axes being parallel 
with the long diameter of the egg (fig. 158). As at an earlier stage, the nucleolus is 
vesiculated and almost always found lying close to the nuclear membrane, as if it had 
fallen of its own weight like a shot in a bag. 
