356 AIMEE S. VANN>EMAN 



in the act of leaving the ventral, intestinal wall to enter the 

 surrounding mesenchyme tissue. They are amoeboid in shape. 



5. In the 5- and 6-mm. embryos, the germ cells appear at 

 the base of the well-developed mesentery, usually not below the 

 level of the three blood vessels of that region. They are also 

 present in the loose mesenchyme under the aorta, and en route 

 to the germinal epithelium, which has not yet thickened. 



6. In the 10-mm. embryo, the germ cells are established in the 

 indifferent gonad. They are slightly enlarged, preparatory to 

 division. 



7. A study of early stages suggests that germ cells may arise 

 from certain cells of the blastocyst entoderm (yolk-sac entoderm) 

 during secondary bud formation. 



8. The path of migration is from the embryonic entoderm into 

 the intestinal wall, thence into the surrounding mesenchyme to 

 the mesentery, and onward into the germinal epithelium. No 

 germ cells are found at any stage in the blood vessels. 



9. It may be concluded that the germ cells of the four em- 

 bryos of one vesicle do not have a common origin, in the sense 

 of having arisen from a prelocalized region of the early plastocyst. 



BIBLIOGRAPHY 



Allen, B. M. 1906 The origin of the sex-cells of Chrysemis. Anat. Anz., 



Bd. 29. 



1907 An important period in the history of the sex-cells of Rana 



pipiens. Anat. Anz., Bd. 31. 



1911 Origin of sex-cells of Amia and Sepidosteus. Jour. Morph., 



vol. 22. 

 Beard, J. 1900 The morphological continuity of the germ cells of Raja bates. 



Anat Anz., Bd. 18. 



1902 The germ cells of Pristuirus. Ibid. 21. 

 Berenberg-Gossler, H. von 1912 Die Urgeschlechtszellen des Hiihner- 



embryos u. s. w. Arch. Mikr. Anat., Bd. 81. 

 DoDDS, G. 1912 Segregation of the germ, cells of the teleost Sophius. Jour. 



Morph., vol. 21. 

 EiGENMANN, C. 1896 Sex dinerentiation in the viviparous teleost Cymato- 



gaster. Arch Entwich., Bd. 4. 

 Federow, V. 1907 Ueber die Wanderung der Genital-Zellen bei Salmo Fario. 



Anat. Anz., 31. 

 Fuss, A. 1912 Ueber der Geschlechtszellen der Menschen und der Saugetiere. 



Arch. Mikr. Anat., Bd. 81. 



