582 Gideon S. Dodds. 



c. Early period. Under this heading will be described the 

 germ-cells of embryos younger than stage 9. About this period 

 centers the greatest interest of the present studies, because such 

 stages mark the only gap in our knowledge of the germinal cycle 

 of vertebrates. In these early embryos it becomes increasingly 

 difficult to distinguish between germ-cells and somatic cells, and 

 in no vertebrate has the germ-cell line been traced back to the 

 unsegmented egg. In Lophius germ-cells were not recognized in 

 embryos younger than stage 6. 



The germ-cells of this period bear a very close resemblance in 

 all features to those of stages 9-13 previously described. Their 

 outlines are rounded and more distinct than those of body cells; 

 their nuclei are irregular in shape and each has two small plas- 

 moson:es quite far apart and close to the nuclear membrane as in 

 older embryos. The germ-cells are, however, in the early period 

 but little larger than other cells and stain almost as deeply, which 

 conditions make them difficult to recognize. In searching for 

 them in the sections the difference in the plasmosomes is the only 

 feature which readily strikes the eye and accordingly it was to 

 this feature more than to any other that attention had to be di- 

 rected in tracing the germ-cells in the early stages. 



In stages 1 and 2 the plasmosomes of all cells are small (figs. 

 19 and 20) suggesting the germ-cells of embryos a little older, and 

 I first thought that possibly the condition in the germ-cells was 

 primitive, persisting from these early stages. This seemed the 

 more reasonable because it is a matter of general observation that 

 the germ-cells of vertebrates actually do retain primitive charac- 

 ters longer than other cells of the embryo. Careful search, how- 

 ever, failed to reveal in any embryo of stages 3, 4 or 5, a single 

 cell which showed this or any other recognizable character of germ- 

 cells. Their line could not be traced back by this character as I 

 had hoped it might. 



In all embryos of stages 6 and 7 a small number of germ-cells 

 could be recognized, and once found there was seldom any diflft- 

 culty in being certain about their identity, but the most careful 

 search failed to reveal in embryos of these stages as many of them 

 as there were in older ones. A glance at table 1, page 578, shows 



