592 Gideon S. Dodds. 



« 



noticeable at the time of the extrusion of the plasmosome. It 

 hardly seems possible that the volume of plasmosome material 

 lost to the nucleus at this time is sufficient to account for the 

 shrinkage, but possibly at the same time other substances are 

 also lost, and the nuclear membrane is in such a condition that 

 they are not renewed. More recent physiological research has 

 shown that changes in permeability of the membranes of the cell 

 have much to do in determining its physiological condition. It 

 may be that during the rest stage, the germ-cells of Lophius are 

 characterized by a condition of impermeability of the nuclear 

 membrane. 



The above discussion of conditions observed in these cells dur- 

 ing the rest period offers still no explanation why this period of 

 suspended activity begins, nor w^hy, after a time it comes to an 

 end. At its beginning, before there are any differences we can 

 detect with the eye, there must be an unseen physiological dif- 

 ference which determines the future behavior of the cell. What- 

 ever the nature of this difference it is one of the earliest of which 

 we have evidence in the cleaving egg of Lophius. 



/. Nuclear processes in germ-cell segregation. A process simi- 

 lar to the extrusion of plasmosome material from the nucleus of 

 the germ-cells of Lophius has not been observed in any other ver- 

 tebrate. As described in other vertebrates, the first differences 

 between the two groups of cells arise gradually and seem due to 

 changes in the body cells rather than in the germ-cells. In Lo- 

 phius, on the other hand, the first differences which enable us to 

 recognize the germ-cells arise suddenly by nuclear changes within 

 them. This feature of the early development of Lophius recalls 

 nuclear changes of a somewhat similar nature which have been 

 observed at the time of the first segregation of the germ-cells of 

 invertebrates of various groups. The best known of these cases 

 is that of Ascaris megalocephala described by Boveri ('92) and 

 since verified by many others. During each of the four first 

 cleavages there is a throwing off of chromosome ends from 

 the nucleus in a single blastomere. At the fourth cleavage 

 the blastomere containing the undiminished amount of chro- 

 matin is the first germ-cell. Three other species of Nematodes 



