MIGRATION OF GERM CELLS IN AMIURUS NEBULOSUS. 353 



thirty-one days he found germ cells in the same position. After 

 the ccelome is formed he found the cells in both somatopleure 

 and splanchnopleure in one embryo 13 in the somatopleure, 4 

 in the splanchnopleure and 3 between these layers. 



In salmon embryos the number of germ cells remains constant 

 up to 185 days after fertilization. But this number varies from 

 20 to 54. In an embryo of 154 days he found 46 germ cells, in 

 one of 185 days, 234 cells, in one of 199 days, 373 cells. The 

 most posterior germ cell is six or seven somites anterior to the 

 anus. As the embryo develops the nuclei enlarge to some extent 

 so that the ratio of the diameter of the nucleus to that of the 

 cell becomes somewhat greater. The nucleus has a sharper 

 contour, loses its granular appearance and shows small chromatin 

 bodies. From 46 to 50 days after fertilization the first small 

 nucleoles appear, later they are larger, stain more deeply and 

 increase in number. 



The genital ridge arises as a discontinuous thickening of the 

 ccelomic epithelium in the region of a germ cell. The thickenings 

 unite and others are formed anteriorly and posteriorly. The 

 uniting of these thickenings takes place at about 60 days. By 

 82 days the ridge is continuous in the gonal part of the embryo and 

 is represented in the progonal and epigonal region by separate 

 thickenings. The end of the genital ridge is posterior to the 

 anus in one salmon embryo. The genital fold rises disco n- 

 tinuously. The ccelome cells of the genital ridge pull apart and 

 leave a space in which there is a fluid. This fold extends pro- 

 gonally and epigonally and ends in the genital ridge. 



In agreement with Nussbaum and Jungersen, Bohi found the 

 genital fold to be composed of epithelial cells and not as MacLeod 

 had observed it a group of germ cells on the surface of the 

 epithelium. Bohi believed the ccelome cells to give rise to (a) 

 indifferent cells, (&) follicle cells, (c) germ cells. The cells on 

 the sides of the genital fold gradually become transformed into 

 germ cells. This changing of epithelial cells into germ cells lasts 

 for only a short time and in embryos of 277 days no more transi- 

 tion cells can be found. The epithelial cells next to the germ 

 cells are converted into follicle cells by pressure of the germ cells 

 against them. According to Bohi some of the germ cells are 



