326 A. RICHARDS AND JAMES T. THOMPSON. 



migration of the primary sex-cells is reduced to a mere phylo- 

 genetic vestige and is without any great genetic significance. 

 Firket speaks of the primordial germ-cells as " primary genital 

 cells " which, after migration disintegrate in the germ gland, 

 being replaced by the true of " secondary genital cells " which 

 arise from the peritoneal cells of the germ gland. Von Beren- 

 berg-Gossler regards 'them as mesodermal wandering cells of late 

 endodermal origin, and describes them as contributory in the for- 

 mation of the Wolffian ducts. 



In our study of this general problem in Fundiilus a number of 

 questions have arisen as separate phases of the matter. The blas- 

 tomeric origin of the sex-cells, their path and method of migra- 

 tion, and their history after reaching the germ gland are all mat- 

 ters requiring separate study. This paper has, as its special aim, 

 the definite identification of the primary sex-cells and the deter- 

 mination of the germinal path in Fundiilus embryos ; that is, it 

 is concerned with the second question listed. As yet our data 

 upon the first question is inadequate and we have not enough 

 material for a study of the third. 



MATERIAL AND METHODS. 



The material for this investigation consisted of the eggs of the 

 teleost, Fundiilus hctcroclitus and was collected at Woods Hole 

 in the summer of 1919. Care was exercised to insure an approxr 

 mately uniform fertilization of the ova by mixing them with 

 chopped testis. Two extensive series w^ere preserved during the 

 summer. Although accurate records were kept as to the age of 

 each group, they are of only jiominal value in this investigation, 

 since environmental and individual differences cause variations in 

 development of embryos of like age. 



All embryos in these two series were fixed in Bouin's fluid and 

 stained by the familiar " long method " for iron haematoxylin. 

 Other material in various fixatives was also available for com- 

 parison. No trouble was experienced in obtaining slides which 

 show clearly the cytological characteristics throughout the series 

 as far as described. A majority of sections were cut 4 micra thick, 

 but some were cut 5, 6 and / micra. The thickness of all sections 



