342 ALBERT KUNTZ AND O. V. BATSON 



roots are entirely absent in at least sLx successive segments. Nev- 

 ertheless, synipathtic primordia related to the ventral roots of 

 the spinal nerves are present bilaterally in all of these segments. 



Figure 3 is reconstructed from several sections from one of the 

 segments in this series. In order to show approximately what 

 portion of the neural tube is wanting at this level, a camera lucida 

 outline of the cross section of its remnant is superimposed 

 (fig. 3, A) on a camera lucida outline of the same magnifica- 

 tion of a cross section of the neural tube taken several segments 

 farther cephalad where it was not affected by the operation. As 

 indicated in figure 3, a small aggregate of cells of nervous origin 

 which is not incorporated in the wall of the neural tube lies along 

 one of its dorsolateral aspects in the segment from which this 

 figure was taken. Apparently a few cells migrate from this cell- 

 aggregate along the ventral nerve-root. In view of the exten- 

 sive destruction of the nervous tissue which occurred at this 

 level it is quite improbable that these are cells of neural crest 

 origin. They probably represent cells of medullary origin which 

 became somewhat displaced by the operative procedure and did 

 not again become incorporated in the wall of the neural tube. 

 No cells suTiilarly located were observed on the opposite side in 

 the same segment nor on either side in any of the other segments 

 in this series. As indicated in the figure, the sympathetic pri- 

 mordia in this instance are relatively small and somewhat 

 asymmetrical. 



Number 4. In this embryo the operation involved the nerv- 

 ous system from the level of the anterior to the level of the 

 posterior limb-buds. The destruction of tissue was somewhat 

 more extensive in this case than in any of the others. In several 

 segments in the anterior portion of the region involved the central 

 nervous system is represented by a very slender column of nerv- 

 ous tissue in which there is no neural canal. Advancing caudad 

 the remnant of the neural tube becomes somewhat larger and 

 contains a small neural canal. Farther posteriorly it again be- 

 comes smaller until at a level just anterior to the posterior 

 limb-buds the central nervous system is entirely absent. Spinal 

 ganglia and dorsal nerve-roots are absent bilaterally in every 



