338 ALBERT KUNTZ AND O. V. BATSON 



were successfully destroyed these parts are not restored. Most 

 commonly the remnant of the neural tube as repaired contains a 

 single small neural canal which is lined by an ependymal layer. 

 At certain points an attempt at duplication occurred in which 

 two small neural canals were formed. At some points the opera- 

 tive procedure apparently caused some displacement of masses 

 of nervous tissue which continued to live. At such points may 

 be observed the rudunents of three or four distorted neural canals. 



In one of the embryos which were killed at the close of the 

 fourth day of incubation development was materially retarded; 

 in the other only the posterior portion of the trunk was involved 

 in the operation. In one of the other embryos the destruction 

 of tissue was not sufficiently extensive to insure the complete 

 absence of spinal ganglia except in a few segments on one side 

 only. These three embryos were discarded for the purposes of 

 this study. The following observations are based on prepara- 

 tions of the four remaining embryos all of which were killed at 

 the close of the fifth day (120 hours) of incubation. 



Number 1. In this embryo the operation involved the nerv- 

 ous system throughout the lower thoracic, lumbar and sacral 

 regions. The destruction of tissue occurred asymmetrically. 

 In the thoracic region spinal ganglia and dorsal nerve-roots are 

 absent unilaterally in four successive segments. In the next 

 two segments the spinal ganglia are represented by small aggre- 

 gates of ganglion cells and the dorsal nerve-roots by relatively 

 few fibers. Continuing caudad spinal gangha and dorsal nerve- 

 roots are completely absent on the same side in several succes- 

 sive segments. Spinal ganglia and dorsal nerve-roots are present 

 on the opposite side in all of these segments. In some segments 

 they are approximately of normal size; in others they are 

 materially reduced. The primordia of gangha of the sympathetic 

 trunks are present bilaterally in all of these segments. Obviously, 

 the primordia of the sympathetic ganglia which are associated 

 with those spinal nerves which are represented by the ventral 

 roots only arose from cells which advanced from the neural tube 

 along the paths of these ventral nerve-roots. Farther posteri- 

 orly the destruction of nervous tissue was more extensive, and 



