MIGRATION OF GERM CELLS IN AMIURUS NEBULOSUS. 355 



ridge in the dorsal end of the mesentery. This ridge divides 

 anteriorly into two ridges each of which end in a single little 

 fold of the peritoneum which is differentiated only by being 

 rich in nuclei. In some larvae at this time the germ cells have 

 not increased in number, in others they may have divided once. 

 In one larva in which a few cells were widely separated from the 

 majority, the ridge entirely disappeared to reappear in the 

 neighborhood of some widely separated anterior cells. From 

 such instances it is evident that the germinal ridge develops 

 only under the influence of the reproductive cells. 



Dodds ('10) in Lophius was able to recognize germ cells when 

 the blastoderm had not quite half covered the yolk. At this 

 time they are in the primary entoblast. They pass into the 

 mesoblast when this is separated and into that part which 

 becomes the myotome. Later when the mesoblast is separated 

 into myotome and lateral plate the germ cells migrate into the 

 latter and again when this splits they are left in the splanchno- 

 pleure. Later they migrate toward the median border of the 

 ccelome and thence upward into the somatic layer and to the 

 position of the permanent germ cells. 



The number of germ cells varies but is small not over fifty- 

 five. From the time they are recognizable until they are in the 

 position of the germ gland there is no increase in number. The 

 apparent increase in early stages is due to changes in the cells 

 which make them more easily recognizable. The cells are 

 characterized by rounded outlines or they may be amoeboid. 

 The cytoplasm stains more deeply than that of the somatic cells, 

 the nucleus is smaller, irregular in shape, apparently less turgid 

 and contains two small nucleoles. The nuclei of the somatic 

 cells have two large nucleoles or a single very large nucleole. 

 The decrease in the size of the germ cell nucleoles is due to a loss 

 of part of their content through the nuclear membrane into the 

 cytoplasm. This extrusion of nuclear material does not take 

 place simultaneously from the nucleoles of any one nucleus nor 

 from all germ cells. 



There is no segmental arrangement of the germ cells. There 

 is both an active migration of the cells and a passive change due 

 to growth of the surrounding tissue. Dodds is of the opinion 



