282 JORDAN. [Vol. VIII. 



Origin and Development of the Ovum as a Whole. — I have 

 not yet completed my study of the differentiation of the germ- 

 cells in the larva, and shall confine myself here to a brief de- 

 scription of the formation of the ova in the mature female. In 

 the adult, as has been stated, the ova arise between two folds of 

 epithelium and originate directly from the epithelial cells of 

 the outer or so-called germinal epithelium (Fig. 4, PI. XV). My 

 observations on this point agree substantially with those of 

 Iwakawa ('82), and I have frequently found in silver nitrate 

 preparations appearances like those figured by him in Figs. 3, 

 5, and 6, PI. XXII. The epithelial cells that give rise 

 to ova are to all outward seeming exactly like the other 

 peritoneal cells. As soon as the germ-cell becomes recogniz- 

 able as such, other epithelial cells are seen crowded around it, 

 and eventually some of these form the follicle cells of the young 

 ovum. 



I have not been able to determine to my own satisfaction 

 whether follicle cells and ovum originate immediately from a 

 single germinal epithelium cell, or whether the young ovum is 

 a lineal descendant from a primordial ovum and the follicle 

 cells from primordial follicle cells. Considered cytogenetically, 

 however, both follicle and ovum, if the line of cell descent only 

 be pushed back far enough, must have had a common origin 

 from a single cell somewhere in the developmental history of 

 the larva. There is no valid morphological support for a belief 

 in an early analysis into definite ova on the one hand and into 

 definite follicle cells on the other, and I can see no inherent 

 improbability in the view that the analysis into ovum and 

 follicle occurs at a comparatively late stage in the develop- 

 ment of the germinal epithelium. 



At the same time, however, I incline to the view taken by 

 Iwakawa ('82) and Hoffmann ('86) that the follicle takes its rise 

 from the germinal epithelium contemporaneously with the 

 ovum, and that follicle and ovum do not have immediate origin 

 from the same cell. Fig. 4 shows a well developed ovum, with 

 the follicle cells just beginning to grow over it from the super- 

 jacent epithelium, and indicates a condition similar to that 

 described by the observers just cited. The cells of the 



