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BULLETIN OF The BUREAU OF FISHERIES. 
ductive habits, and it is remarkable how quickly this crustacean can on occasion adapt- 
itself to new conditions, as seen in the successful transportation of the lobster 12,000 
miles through the Tropics to New Zealand in 1906-8 (see p. 176). 
The history of the ovary will now be considered on the basis of the periodic events 
noticed above and as they have been found to occur on the coast of Massachusetts. 
DEVELOPMENT OF THE OVARY TO THE FIRST SEXUAL PERIOD. 
The ovaries (pi. xlv) are first recognized in well-advanced embryos as minute paired 
ovoidal masses of mesoblastic cells below the forward end of the heart and close to the peri- 
cardial wall. Later they appear as solid rods composed of a wall or capsule and a lining 
epithelium. The ovaries do not originate as hollow tubes, but virtually possess a tubular 
structure at the time the ripe eggs are expelled by contractions of their muscular walls. 
Egg laying is followed by a collapse of these walls and the immediate return of the 
ovary to a solid condition. It will, however, be easier to understand the structure 
eventually attained by conceiving the organ as possessed of a tubular form, the entire 
wall of which is composed of two parts, namely, (a) a capsular layer consisting of invol- 
untary muscle, connective tissue, blood vessels and sinuses, and ( b ) a lining epithelium. 
Between these parts the blood finds ready access in irregular channels after leaving its 
definitive vessels. The ovarian epithelium consists of a basement membrane and epithe- 
lial cells from which the eggs and egg follicles are differentiated (fig. 1, pi. xlvi). The 
superficial area of this epithelium becomes greatly increased by irregular inwardly directed 
folds or invaginations. Through the reentrant sinuses thus formed blood penetrates to 
every part of the organ. The egg follicles are eventually composed of a thin sheet of 
tissue, the cells of which, as we have seen, are homologous with the ova. These follicles 
separate each egg from its fellows, form a medium for the transfer of nourishment to it 
from the blood, and soon begin to secrete about it the transparent egg shell or chorion. 
Owing to the manner in which the invaginations of the ovarian epithelium arise, the 
ova at a certain stage are arranged in irregular, radial and longitudinally directed tiers; 
each tier is embedded in opposing sheets of follicular tissue, while each ovum is com- 
pletely inclosed, and the largest and oldest eggs are peripheral. 
Along the central ridges of the epithelial folds the primitive ovarian cells mulitply 
and become differentiated into the future ova and follicular elements which are crowded 
or discharged into what corresponds to the lumen of the ovary, or into its central parts. 
(Fig. 5, pi. xlv.) 
The process of early differentiation and growth of the eggs seems to proceed in the 
following manner (fig. 1, pi. xlvi) : Along the crests of the central folds referred to above, 
the ovarian cells become columnar and often greatly elongated; each narrow cell appears 
to be attached to a corresponding thickening of the basement membrane, which forms 
the lining of a blood sinus. To this is due the “pitted appearance’’ mentioned by 
Bumpus ( 41 ). The nucleus of a cell destined to become an egg, which lies close to the 
basement membrane, swells into a large spherical vesicle, about which a thin layer of 
cytoplasm, without boundary wall, may be discerned. Granules of yolk appear almost 
