:^ J. M. ESSENBERG. 



cytoplasm; the nucleus is elongated and may be more or less ir- 

 regular in contour. The chromatin is granulated and an ill-defined 

 nucleolus can occasionally be noticed. The nuclei take a dark stain 

 and contrast strikingly with the germ cell nuclei. The first sign 

 of such metamorphosis appears to be the activity of the chromatin 

 in which the granules become coarser, forming more or less into 

 lumps. This phenomenon is closely followed by the growth of 

 nucleus and cytoplasm. The elongated and irregular contour be- 

 comes regular and the stain loses its density. The final product of 

 such transformed epithelial cells can not in any way be distin- 

 guished from primordial germ cells (Figs. 1-2). As these cells 

 increase in size they passively move from the epithelium into the 

 cortex of the ovary to develop into follicles. Fully formed germ 

 cells do occur in the epithelium, which will be discussed later. The 

 transformation of epithelial cells into germ cells is by no means a 

 rarity. It is a common occurrence in all phases of ovarian activity 

 of the females belonging to class i. Occasionally a place in the 

 epithelium may be found where all stages of such transformation 

 occur in the same field of the microscope. Such a condition is 

 found in Fig. 12. At least six definite stages (a-f) are shown in 

 the figure which range from epithelial to completely formed germ 

 cells. 



It will be remembered that the epithelium of the ovarian cavity 

 originates from the peritoneal lining of the fusing gonads, and that 

 no germ cells whatever enter into its composition at any time. 



The formation of germ cells from epithelium of the ovarian 

 cavity is by no means confined to Xiphophorus hclleri among the 

 teleosts. Similar observations have been made by Hoffmann 

 (1886) and Bohi (1904) on salmon, Wallace (1904) on Zoarces 

 viz-iporus, Philippi (1908) on Glandichthys januarius, et al. 



After the transformation process of the epithelium cells into 

 germ cells was discovered, it became apparent that such transforma- 

 tion may occur at any place in the ovary directly from the free 

 cells of peritoneal origin (Fig. 15, tpc}. The process is the same 

 in principle as described above. 



