60 



right side, and soon disappears. From the middle of the Wolffian 

 body to the end of embryo, the cord is entirely normal (Fig. 6). 



Fig. 6. C. S. Normal cord after disappearance of secondary canals. 



The spinal cord of this abnormal chick presents a series of 

 secondary neural canals, or more properly vesicles, which appear and 

 disappear over and over again. None of these canals open into one 

 another, and none of them run into the central canal. All of them 

 are lined with the same kind of cells that line the central canal. 

 Their origine and meaning are puzzles. But the fact that the central 

 canal becomes smaller, the more numerous are the secondary canals; 

 that the central canal elongates along a path of specialized tissue 

 running between it and the last important secondary canal; and that 

 the secondary canals are lined with the same tissue that lines the 

 central canal, these facts, taken together, seem to indicate that the 

 secondary canals arose as outgrowths from the central canal, although 

 at this time they are quite unconnected with it. The cause of such 

 outgrowths as the central canal is entirely unsuspected, for all the 

 eggs were treated in the same way, and all the other embryos were 

 quite normal. 



University of Pennsylvania, Philadelphia, 

 June 1898. 



Abgeschlossen am 6. September 1898. 



Frommannsche Buchdruckerei (Hermann Fohle) in Jona, 



