360 



FREDA M. BACHMANN. 



EMBRYOS 7 MM. LONG. 



Three embryos of this length were sectioned. In one of these 

 there were 26 germ cells most of which were in the mesentery or 

 at least very near it (Fig. 6). In the other two embryos the 

 germ cells had probably divided once although there was little 

 difference in the size of the cells from those in earlier stages. The 

 cells were 14-16 microns in diameter and the nuclei 7-8 microns. 

 There were 57 cells in one embryo and 63 in the other. In both 

 embryos most of the germ cells were crowded in the mesentery 

 in nests of 3 to 8 (Fig. 7). A few single cells were nearer the germ 

 gland anlage or still in the splanchnopleure. Except in the case 

 of one cell dividing, the appearance of the nuclei, cytoplasm, etc., 

 seemed the same as in cells in earlier stages. The germ cells 

 are in the same region as in the 5 mm. stage. The following 

 table gives the number of cells, the length throughout which the 

 cells were distributed, the distance anterior to the anus of the 

 most posterior cell, and the distance anterior to the tail region 

 of the most anterior cell. 



EMBRYOS 9 MM. LONG. 



In embryos of this length the anlagen of the germ glands appear 

 as a fold in the peritoneum on either side of the base of the 

 mesentery. (Figs. 8 and 9). This fold extends from 0.030 to 

 0.280 mm. anterior to the most anterior germ cell. In one em- 

 bryo the fold was poorly developed for a distance of 0.080 mm. 

 where there were no germ cells but this is not the most common 

 condition. After the fold once appears, it is continuous through- 

 out the region in which the germ cells are found. In one embryo 

 there were no germ cells for a distance of 0.200 mm. but in this 

 entire distance the fold of the peritoneum was very prominent. 

 The fold seems to extend as far posterior from the germ cell region. 

 It was found to extend 0.080 to 0.230 mm. posterior from the 

 most posterior cell. In all of the embryos of this stage which 



