ORIGIN OF PRIMORDIAL GERM CELLS 515 



vessels of the head. This is an abnormal condition, since the 

 germ-cells in all the other embryos studied, are never grouped 

 in this way. The embryo with 25 somites is the oldest in which 

 germ-cells are found in the vessels. 



The embiyo with about 22 to 23 segments is the youngest in 

 which the primordial germ-cells have hitherto been described in 

 the bird. NusslDaum ('80) and Keibel and Abraham ('00) in 

 the chick, and HofTmann ('93) in Gallinula, Sterna and Haema- 

 topus described the germ-cells at 23 somites in the splanchno- 

 pleure. 



6. In embryos possessing about 26 to 29 somites the primor- 

 dial germ-cells are found in the splanchnic mesoderm near the 

 radix mesenterii. 



7. In embryos with 30 to 33 somites the primordial germ-cells 

 are in the radix mesenterii and coelomic epithelium on both sides 

 of the coelomic angle. They remain in this position until the 

 formation of the gonad begins when they gradually pass into 

 that organ. 



BIBLIOGRAPHY 



Allex, B. ^I. 190.) The origin of the sex-cells of Chrysemis. Anat. Anz., Bd. 



29. 



1909 The origin of the sex-cells of Amia and Lepidosteus. Anat. Rec, 



vol. 3. 

 Beard, ,J. 1904 The germ-cells. Part 1. Journ. Anat. and Phys., vol. 38. 

 Bensley, R. R. 1911 The pancreas of the guinea-pig. Amer. Jonr. Anat., vol. 



12, pp. 297-388. 

 VON Berenberg-Gossler 1912 Die Urgeschlechtszellen des Hiihnerembryos 



aus 3 and 4 Bebriltungstage. Arch. Mik. Anat., Bd. 81. 

 B.\LBIANI, E. G. 1885 Contribution a I'etude de la formation des organes sexuels 



chez les insectes. Recueil Zoologique, Suisse. 

 Dantschakopp, W. 1908 Entwicklung des Blutes bei den Vogeln. Anat. Hefte, 



Bd. 37, S. 471. 

 d'HoLLAXDER, F. 1904 Recherches sur I'oogenese et le noyau vitellin de Bal- 



biani chez les oiseaux. Arch. d'Anatomie Mic, T. 7. 

 DoDDS, G. S. 1910 Segregation of the germ-cells of the tclcost Lophius. Jour. 



Morph. vol. 21, p. 563. 

 EiGEXMANN, C. H. 1892 On the precocious segregation of the sex-cells in Cyma- 



togaster. Journ. ^Nlorph., no. 5, p. 481. 



1897 Sex differentiation in the viviparous teleost Cymatogaster. Arch. 



Arch. f. Entw'mech., Bd. 4, p. 125. . 



