494 J. BRONTE GATENBY 



matter was dit'ticult to docido. In none of the pivparations 

 could distinct cell-walls be found in the follicle at the period 

 when the zona substance was beginning to appear. There is 

 no doubt in my mind that the substance of the zona is formed 

 in direct relationship to the cells of the follicle, and the cyto- 

 plasm of the egg probably takes merely a secondary or stimu- 

 latory part in the; production of this important membrane. 



T\w mitochondria, so far as they could be followed out, 

 act in the same manner as in both the fowl and the frog, and the 

 young oocyte contains the same formed elements as that of 

 the fowl, i. e. sphere, centrioles, and cloud of mitochondria. 



17. Bibliography. 



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3. Caldwell, W. H. — " The Embryology of the Monotremata and Mar- 



supialia ", ' Phil. Trans. Roy. Soc.', 1887. 



4. Semon, R. — " Beobachtungen iiber die Lebcnsweise und Fortpflanzung 



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 1894. 



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 1911. 



6. Wilson, J. T., and Hill, J. P. — " Observations on the Development of 



Ornithorhynchus ", ' PhU. Trans. Roy. Soc.', 1907. 



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' Jenaische Zeitsch.', 1885. 



8. Thing, A. — " The Formation and Structure of the Zona Pellucida 



in the Ovarian Eggs of Turtles ", ' Amer, Journ. Auat.', vol. 23, 

 1918. 



9. Gateiiby, J. Bronte. — " The Transition of Peritoneal Epithelial Cells 



into Germ-cells". &c., ' Quart. Journ. Micr, Sci.', 1915. 



10. Van Durme. — " Nouvelles recherches sur la viteUogenese des oeufs 



d'oiseaux ", &c., ' Arch, de Biol.', tome xxix, 1914. 



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