The Germ-cells of Lophius. 591 



the phenomenon of arrest of cleavage, but it in no way explains 

 the mechanism by which it is brought about. 



The conditions observed in Lophius point very clearly to this 

 as a period of arrested activity of the germ-cells, during which, 

 for some reason the metabolic processes of the cells are relatively 

 low. The arrest of mitosis is of itself an evidence of suspended 

 activity. The small size of the nucleoli is also in all probability 

 an indication of the same condition. It is I believe quite gener- 

 ally agreed that the size of the plasmosome is in some measure 

 an index of the activity of the cell. Whether the extrusion of a 

 part of the plasmosome material from the nucleus, is also an evi- 

 dence of lowered metabolic activity of the cell, I cannot say. It 

 indicates at any rate some important physiological difference. 



Every nucleus, at mitosis, gets rid of its plasmosome mate- 

 rial. There are also cases on record of an extrusion of plasmosome 

 material from the resting nucleus, and this extrusion seems depend- 

 ent upon the activity of the cells, as if the substance accumulated 

 so rapidly that there was need to get rid of it between divisions. 



The conditions of extrusion from the resting nucleus of the 

 germ-cell of Lophius, however, seems to be entirely different, 

 and not at all a manifestation of high activity. In the germ-cells 

 of Lophius there is for a long time after extrusion of plasmosome 

 material no increase in the size of the nuclear plasmosome remain- 

 ing. In the somatic cells during stages 6-14 the amount of 

 nucleolar material produced in the resting nucleus and lost during 

 the many divisions must be considerable, while during the same 

 period little or none is produced by the germ-cells. 



The shape of the nucleus is also a probable indication of sus- 

 pended activity in the germ-cells. In very active cells it is likely 

 to be very irregular, sending out amoeboid processes, which pre- 

 sent a large surface for the exchange of substances between nucleus 

 and cytoplasm. The irregularity of the nucleus of the germ-cells 

 of these embryos is of a different nature. They present rather a 

 shrunken appearance,, as if cessation of activity had allowed the 

 nuclear sap to diminish, leaving the nuclear membrane too large. 

 This shrunken appearance, as pointed out above, first becomes 



