290 BULLETIN OP 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 HRST 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 

 epitheUum. 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 (6) a lining epithehum. 

 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 folUcles are differentiated (fig. i, 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 folUcular 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. i , 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 



