160 Harry Lewis Wieman. 



beginning of the growth period of the ovocytes, their formation 

 is undoubtedly connected with the functional activity of the 

 nurse cells. 



Those of the primordial germ cells that develop into functional 

 ova are not grouped into cysts, and epithelial cells are scattered 

 among them very irregularly (Figs. 6, 7, 8, 9, etc.). 



The formation of cysts does not have anything to do primarily 

 with the differentiation of the primordial germ cells into nurse 

 cells on the one hand and egg cells on the other, for in the testis 

 where a similar process of cyst formation occurs, the cells thus 

 inclosed develop into functional spermatozoa. Therefore the proc- 

 ess of encystment can not be fundamentally antagonistic to the 

 development of functional germ cells. In the case of the ovary, 

 the differentiating factor has already operated before the cysts are 

 formed. 



In the course of cyst formation in the more distal part of the 

 tube, one frequently sees mitosis and amitosis going on side by 

 side (Fig. 13). It is interesting to note that here mitotic figures 

 are never found inside of definitive cysts, where the multiplication 

 of nuclei always takes place by the amitotic mitotic method. The 

 products of mitotic cell division are single cells. The occurrence 

 of irregularities, such as shown in Fig. 19, has been alluded to. 



Aside from the absence of the mitotic division apparatus, the 

 amitotic division figure is characterized by the fact that the nuclear 

 membrane persists throughout the entire process (Figs. 20, 21, 

 22, 23). Further, the chromatin of the nucleus, which is in the 

 form of rounded granules embedded in a reticular network, is separ- 

 ated from the nuclear wall by a clear space that disappears 

 when, the nucleus comes to rest after division (cf. Fig. 16). 



The first authentic case of amitosis in the insect ovary seems 

 to have been noted by Mayer (75), who observed the occur- 

 rence of doubly-nucleated cells in the follicular epithelium of 

 Pyrrochoris apterus. A little later, Brandt ('78) described in the 

 nurse chamber of Septura rubratisturea" hisquii formige Kerneauf- 

 treten die auf Theilungen hindeuten." Will ('85) described simi- 

 lar divisions of the nurse cells in Nepa and Notonecta, and used the 

 facts to good advantage in developing his "Ooblasten" theory. 



