Spinal Canal in Chick Emhri/os. 155 



take place with some rapidity, as amongst the large number 

 examined I have never seen a trace of subdivision after the fifty- 

 eighth hour. 



In conclusion, I wish to thank Professor Baldwin Spencer for 

 his help and encouragement, and the use of his laboratory, and 

 also to thank Dr. Georgina Sweet for the kind assistance she has 

 given me. 



BIBLIOGRAPHY. 



1. Amelia Smith. — -Multiple canals in the spinal cord of a chick 



embryo. Anal. Anz., Bd. xv., 1899. 



2. Y. Federow. — Zwei Falle von Yerastelung des Zentralkanals 



des Medullarrohres beim Hiihnchen. Anat. Anz., Bd. 

 xxxi., 1907. 



3. G. Cutore. — Anomalia del canale midollare in mi embrione 



di polio di 48 ore. Att. Accad, Gwen. Sc. Nat., Catan. 

 Ser., 4v., 12, 13S. 



4. Mingazzini. — Anomalia dell' extremita posteriore del midollo 



spinale nell' embrione di polio. Bull. B. Ace. Ned. 

 Roma, Anno 25, F 3-7, S 709-718. 



DESCRIPTION OF PLATE XLII. 



Reference letters: — • 



a = amnion. 



e = epiblast, 



h = hypoblast. 



m ^mesoblast. 



n.c. = nerve cord. 



n =notocord. 

 Figs. 1, 2, 3. — Transverse sections of chick embryo at 56 



hours, Fig. 1 being the most caudal and Fig. 3 the most 



cranial, showing the formation of the three canals in the 



nerve cord. 

 Figs. 4, 5. — Sagittal sections through a chick embryo at same 



stage as Figs. 1-3, showing configuration of nerve cord 



and character of the walls subdividing the original single 



canal into three. 



