TRANSPLANTING NEURAL TUBE OF AMBLYSTOMA 181 



there was any indication of any connection between the transplant 

 and the stumps. 



Only twelve operations were made in the F series, and this 

 number is of course too small to serve as the basis for far-reaching 

 conclusions; nevertheless, the fact remains that the results in 

 this series differed consistently from the others in that restora- 

 tion of anatomical and functional continuity was delayed or 

 even excluded. At the time the operations were performed it 

 was not forseen that a matter of a few somites difference in level 

 would make a material difference in the reaction of the neural 

 tube to the operation; but it can be pointed out now that the 

 results obtained are what one should expect if the initial step in 

 the restoration process is a posterior growth of fibers from the 

 brain to the transplanted tube, since the longer time required 

 for fibers to reach the more posterior level would allow somites 

 intervening between transplanted tube and the neural stumps 

 to develop to such an extent as to delay materially, if not actually 

 to prevent, the formation of a nervous connection. Therefore 

 the nearer to the brain the transplantation is made the better 

 the chances for connections being established. This point will 

 be subjected to further experimental test, the results of which 

 will be reported upon later. 



IV 



We may now review in their proper order the various steps 

 involved in the process of restoring anatomical and functional 

 continuity between the transplanted tube and the rest of the 

 nervous system. In the first place, at the time of the operation 

 in the T. R, T, L., and F series, no tracts were established, so 

 that there was nothing to interfere with localized development 

 taking its natural course; and as a result neuroblasts develop in 

 aU parts of the neural tube, including the transplanted portion. 

 Since a stage just before appearance of sensitivity was used for 

 operation in the G series, the first steps in the formation of the 

 primitive somatic sensory and motor tracts had already started 

 in this series. In the second place, whenever in the sectioned 

 embryo a single connection was found between the transplant 



