586 Gideon S. Dodds. 



evident that the process does not take place in all cells at the same 

 time, but that it begins at stage 6 with a few cells and continues 

 until its completion at stage 8. The important point to be made 

 clear in this connection is that it is only as this process progresses 

 that the germ-cells can be recognized and not until its completion 

 can the full number be distinguished. 



A study of the germ-cells of this period indicates that though 

 the full number cannot be recognized until stage 8 the actual 

 beginning of the rest period is somewhat earlier, possibly at stage 

 6 or at the youngest stage 5. That the period of rest does not 

 extend back into younger embroys is evident from the larger 

 size of the cells of these stages. It is in embryos of these stages, 

 5, 4, etc., that we must look for the early multiplication period. 

 At present we are unable positively to identify any germ-cell 

 previous to the extrusion of plasmosome material from the nu- 

 cleus, yet they are unquestionably set apart as germ-cells before 

 this process takes place. 



In stage 6 these cells are to be sought in the primary entoblast 

 where the first cases of extrusion are observed. In this part of 

 embryos of stage 6 there are some cells, not very clearly dis- 

 tinguished from the others, which may possibly be germ-cells 

 prior to the extrusion of plasmosome material. I refer to some 

 cells with nuclei less rounded than the others and having two 

 plasmosomes somewhat separated. Two of these are shown in 

 fig. 21, gf.c? The nuclei of these cells are somewhat indented 

 but are by no means as irregular as those from which plasmosome 

 material has been extruded. Compare these two cells with the 

 germ-cell in the same drawing in which one plasmosome has under- 

 gone decrease of size, and the one in fig. 22 in which both have 

 undergone the process. The location of these possible germ-cells 

 is indicated by open circles in figs. 1 and 2. I do not point to 

 these positively as germ-cells, but simply call attention to the 

 possibility that these are the cells which a little later take on the 

 more obvious distinctive characters of germ-cells. 



From the facts presented in the preceding pages we may draw 

 the following conclusions: 



