ORIGIN OF DEFINITIVE SEX-CELLS 469 



3. Immediately following the formation of the first sexual 

 cords it is possible to determine the sex of the individual being 

 studied (fig. 5). 



In the male the number of primordial germ-cells remaining in 

 the germinal epithelium after the formation of the cords of first 

 proliferation is small, while in the case of the female the number 

 does not seem to be greatly diminished. 



4. Beginning with the 8th, but especially during the 9th, 10th 

 and 11th days of development, there is a rapid increase in the 

 number of primordial germ-cells in the germinal epithelium of 

 the female. Three or four dividing germ-cells may be seen in 

 a small area (fig. 7). Collected into groups, which are the 

 result of successive mitoses, the primordial germ-cells, or oogonia 

 as they may now be called, give rise to lobulations which appear 

 on the deep surface of the epithelium. These lobulations, or 

 buds, composed principally of oogonia, but including also cells 

 of peritoneal parentage, increase in size and become the cords 

 of second proliferation or cortical cords (fig. 8). 



5. The oogonia become the definitive ova, while the peritoreal 

 cells of the germinal epithelium, present in the cortical cords, 

 develop the follicular epithelium. 



BIBLIOGRAPHY 



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1905 The embryonic development of the rete-cords and sex-cords of 

 Chrysemis. Am. Jour. Anat., vol. 5. 



1906 The origin of the sex-cells of Chrysemis. Anat. Anz., Bd. 29. 

 Balfour, F. M. 1878 On the structure and development of the vertebrate 



ovary. Anat. Jour. Mic. Science, vol. 18. 



Bensley, R. R. 1911 Studies on the pancreas of the guinea-pig. Am. Jour. 

 Anat., vol. 12, pp. 297-388. 



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

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 1914 tJber Herkunft und Wesen der sogenannten primaren Urge- 

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BouiN, M. 1900 Histogenese de la glande genitale femelle chez Rana tempor- 

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CowDRY, E. V. 1912 The relations of mitochondria and other cytoplasmic 

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