1922] Phases in the Development of Chrysemys Cinerea 71 



9. Contrary to general opinion, no great care is necessary in 

 handling tnrtles or their eggs, provided uterine eggs or newly laid eggs 

 are used. Embryos may be opened in normal saline without dis- 

 tortion. 



10. Eggs that have been retained by a turtle for a month will 

 produce apparently normal embryos when incubated. 



11. Development in the oviduct ceases about the time the blasto- 

 pore is formed, but may be arrested in the cleavage stages, or may 

 proceed to the first flexure stage. 



12. The rate of development is approximately the same in arti- 

 ficial incubation as it is under normal conditions. There is prob- 

 ably quite a difference in the development rate of various eggs of 

 the same clutch. 



13. Cleavage in Chrysemys cinerea is similar to that of any dis- 

 coidal cleavage form, 



14. In the blastula the lower part is formed by yolk endoderm 

 while the upper part is formed by ectoderm. There is a cavity be- 

 tween them similar to the cleavage cavity of other forms. 



15. In Chelydra serpentina a yolk plug occurs but it does not 

 occur in Chrysemys cinerea. This, with other considerations, indi- 

 cates that C. cinerea is more specialized than Chelydra serpentina. 



16. The rounded blastopore in closing forms first an oval and 

 then a crescent. 



17. The blastopore is formed by an invagination of the ectoderm. 



18. In Chrysemys cinerea, as in Trionyx, the anterior part of the 

 blastoporeal canal forms the archenteron. 



Teinitt College, 

 dxjeham, n. c. 



BIBLIOGRAPHY 



Agassiz, L. 1857. Contributions to the Natural History of the United States. 

 1, Part 11. 



Allen, B. M. 1904. The embryonic development of the rete-cords and sex- 

 cords in Chrysemys. Anat. Lab. Univ. Wis. 1. 



Allen, B. M. 1906-7. A statistical study of the Sex cells in C. marginata. 

 Anat. Lab. Univ. Wis. 3. 



Alten, H. van. 1914. Ueber die Entwicklung des Kiemendarms bei Schild- 

 kroten. Ber. nat. Ges. Freiburg. 1 Br. 20: 99-105. 



Alten, H. van. 1916. Beitrag zur Entwicklung des Kiemendarms einer Schild- 

 krote. Arch. mikr. Anat. 86, Abt. 1 : pp. 585-610. 



Baee von, C. E. 1834. 



