MIGRATION OF GERM CELLS IN AMIURUS NEBULOSUS. 357 



is never aggregated into large masses as is common in the nuclei 

 of somatic cells. 



The germ cells with few exceptions have been found in the 

 mesoderm. These exceptions were a few cells in the coelomic 

 cavity or between the lateral plate of mesoderm and the yolk, 

 also a few doubtful cells in the entoderm. In younger embryos 

 the germ cells are in the lateral plate of the mesoderm and near 

 the region where the blastopore has closed. In older embryos 

 where the tail has grown out beyond the yolk they are in the 

 splanchnopleure surrounding the hind gut. Later they are in 

 the mesentery and in the germ gland anlage. The exact location 

 of the germ cells will be given in greater detail in the description 

 of the different stages studied. 



The number of germ cells is constant until after or about the 

 time they are in the germ gland anlage. The average number is 

 about 23 with extremes 12 and 34. Because of the large size of 

 the germ cells and the thickness of the sections it would be 

 possible to count the same cells twice. However, by noting the 

 position and appearance of the cells and the size of the nucleus, 

 it is believed that few errors have been made in counting. 



There is probably no one characteristic peculiar to germ cells 

 in Amiurus nebulosus. Blood corpuscles are frequently nearly 

 spherical. But in these the cytoplasm stains more lightly with 

 congo red and Orange G., the nucleoles are larger, and the nuclear 

 membrane much more distinct than in the germ cells. Also the 

 ratio of the diameter of the nucleus to the diameter of the cell is 

 greater in blood corpuscles than the same ratio in germ cells. 

 In a number of blood corpuscles this ratio was 2 : 3, in germ cells 

 it is i : 2. The cytoplasm of the entoderm cells often contains 

 much yolk and hence these frequently stain like germ cells. 

 But the entoderm cells are usually smaller and columnar or 

 irregular in shape, and the nuclei are more often oval than spher- 

 ical with two or three large nucleoles. In the earliest stage 

 studied the mesoderm cells were not more than half the size of 

 the germ cells and contained little if any yolk. Even in this 

 stage the nuclei of the mesoderm cells are becoming oval or 

 elongated. In later stages the mesoderm cells are small, very 

 irregular in shape with cytoplasmic processes. The germ cells 



