The Germ-cells of Lophius. 587 



1. There is an extrusion of plasmosome material from the nu- 

 cleus of the primary germ-cells. This marks the beginning of the 

 more obvious characters which enable us to distinguish the germ- 

 cells. 



2. This extrusion of plasmosome material takes place very 

 shortly after the beginning of the period of rest. 



• 3. The process does not take place in all germ-cells simultane- 

 ously. 



4. The reduction of both plasmosomes does not take place 

 at the same time. 



5. Discussion and Conclusions 



a. Means of migration It is now in order to inquire by what 

 means the change of position of the germ-cells of Lophius is ac- 

 complished. Two possible means are suggested by all investi- 

 gators — active migration, and passive change of position due to 

 growth of surrounding tissues. In Lophius, both of these forces 

 seem to be at work. The pulling of the germ-cells into the base 

 of the mesentery at the time of its formation is, for example, 

 brought about by growth of the tissue, while their closer group- 

 ing at this time is very probably due to an active migration. 

 The change from the myotome to the lateral plate is an active 

 migration, and quite a rapid one, and the change of position from 

 splanchnic to somatic mesoblast at a period later, can only be 

 accounted for in the same way. It also seems probable that at 

 an earUer period (stage 6), some of the germ-cells at least migrate 

 from a lateral to a more median position in the primary entoblast. 



It is very commonly recognized that the migrations of germ- 

 cells, in both vertebrates and invertebrates, are accomplished 

 by amoeboid movement, and cells very distinctly amoeboid in 

 shape are often recognized. In Lophius, during most of the 

 period of migration, the germ-cells are decidedly rounded in out- 

 line. The only ones which might be considered amoeboid, were 

 observed in embryos of stages 7 and 8, which, it will be remem- 

 bered, include the period of active migration from the myotome 

 into the lateral plate. In other stages it is not unreasonable to 



