The Germ-cells of Lophius. 579 



From a study of the mimbers given in the above table, one 

 would conclude that stages 6 and 7 mark the early multipli- 

 cation period, and that there is, in these stages, an actual in- 

 crease in the number of germ-cells. A study of the actual speci- 

 mens, however, brings us to the conclusion that there is no increase 

 in number during these stages. For reasons to be given later, 

 it is believed that the full number of the rest period is attained 

 somewhat earlier, probably in stages 5 and 6, though we are 

 unable at this time to distinguish them from other cells in the 

 lower layer of the embryonic area, and that during stages 6, 7 

 and 8 they undergo changes which make them recognizable. 

 This, then, is not a multiplication period, but an early part of the 

 period of rest during which the germ-cells first attain the char- 

 acters by which they may be recognized. 



4. Distinctive Characters of the Early Gerrn-cells 



The germ-cells of most vertebrates so far studied are, up to 

 quite a late stage, filled with deeply staining yolk spherules which 

 cause them to stand out prominently among the surrounding 

 cells. In my preparations they are marked in no such conspicu- 

 ous manner. WTiether this is due to methods of fixation I do not 

 know, but the absence of yolk has made both necessary and pos- 

 sible a somewhat careful study of other features of the cell. 



An account of the structure of the germ-cells of Lophius had 

 best be given in three parts, corresponding to three well-marked 

 periods in the history of the cells themselves. These I will call 

 'early', 'middle', and 'later' periods which mark three divis- 

 ions of the period of rest. 



a. Middle period. For the sake of clearness the middle period 

 will be described first. This includes stages 9-13, during which 

 time the germ-cells do not undergo any appreciable change (figs. 

 29-33). During the same time, however, the surrounding cells, 

 those of the coelomic mesoblast, undergo very marked changes. 

 In stage 9, the germ-cells are but little greater in volume than the 

 surrounding cells (fig. 29) but during further development they 

 remain of the same size, while the coelomic cells become smaller 



