OKLAHOMA ACADEMY OF SCIENCE 15 



VI. THE MIGRATION PATH OF THE GERM CELLS IN 

 FUNDULUS 

 A. Richards and J. T. Thompson 



From the Zoological Laboratory of the L-niversity of Oklahoma. 

 Contribution No. 6, Second Series. 



Investigation of the primary sex cells of Fundulus shows that 

 they may be recognized as early as the forty-six hour stage (1.6 

 mm.), as many as forty-two sex cells having been counted in such 

 an embryo. They were located in the peripheral endoderm, lateral 

 to the posterior half of the embryo. None were observed in that part 

 of the embryo which develops from the head fold. Observations 

 were made upon embryos ranging from one to twenty-four days in 

 age. 



The characteristics of the embryo are distinct and constant 

 throughout all phases of the migration of these cells from the 

 preipheral endoderm to the final position in the genital ridge ; 

 little variation was noted even in their number during the migra- 

 tion period. There can be little reason for ciuestioning the accuracy 

 of the identification of these cells as the "primordial germ cells" 

 of earlier writers. 



The germinal path leads from the peripheral endoderm, into 

 the border of the undifferentiated endodermal cell mass. When 

 this cell mass splits to form gut endoderm and lateral mesoderm, 

 the sex-cells proceed medially with either layer. By the time the 

 gut is formed, these cells are lateral to it ; they all eventually be- 

 come located in the splanchnic mesoderm of this region. From here 

 the sex-cells migrate dorsal to the hind gut, thence to the region 

 ventral to the Wolffian ducts. Here they become svtrrounded by 

 peritoneal cells which form the somatic portion of the gonads. From 

 this position the germ gland anlagen are shifted back to their 

 location dorsal to the gut. 



There is very little multiplication of the sex-cells during the 

 period of migration. Division apparently takes place in the extra- 

 embryonic area, and is not renewed to any marked extent until after 

 the sex-cells become located in the germ glands. 



Migration is passive, being due to forces of growth which are 

 altogether external to the cells themselves. These forces of growth 

 are factors common to the development of the organs formed in 

 the body of the teleost embryo. 



These cells are transported from the edge of the embryonic 

 region medially, to positions just beneath or within the endodermal 

 cell mass, as the case may be. They are carried passively from 

 one position to another by the same forces of growth which result 



