THE AMERICAN LOBSTER. 153 



of eggs of fairly uniform size. The stroma of 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 



fr 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 OF 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 membraue 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. 



Cases 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 161, 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 ^\- 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. 



