66 GERM- CELL CYCLE IN ANIMALS 



provided with a group of about twenty-four meso- 

 derm cells which form a syncytium at the anterior 

 end and may be called nurse cells (Fig. 25, n.c), since 

 they furnish food material to the oocyte. Another 

 group of mesoderm cells forms a cellular layer about 

 the oocyte and nurse cells, and thus constitutes a 

 follicular epithelium. At this stage the oocytes 

 break away from the ovary and become distributed 

 in various parts of the body of the mother-larva. 



Several facts regarding the germ-cell cycle of 

 Miastor deserve special emphasis : (1) There is 

 no stage in the entire keimbahn when the germ cells 

 cannot be distinguished without the least difficulty ; 

 (2) the number of oogonial divisions has been defi- 

 nitely established, and so it is no longer necessary to 

 make the general statement that the germ cells 

 pass through 7i divisions during the period of multi- 

 plication, since here 7i is undoubtedly six; (3) the 

 descendants of the primordial germ cell are only 

 germ cells, i.e., the primordial germ cell does not 

 give rise to both oogonia and nurse cells as seems to 

 be the case in most other insects; (4) chromatin- 

 diminution processes take place during the mitotic 

 divisions of the nuclei from the four- to the eight- 

 cell stage and form the eight- to the fifteen-cell 

 stage of such a nature that all of the cells in the 

 embryo finally are deprived of part of their chromatin 

 with the exception of the primordial germ cell which 

 retains the complete amount of this substance; 

 (5) the primordial germ cell is estabhshed at the 

 eight-cell stage and is the first complete cell formed in 



