182 H. L. WIEMAN 



and the neural stumps, the connection always occurred between 

 the anterior stump and the transplant. Since an outgrowth fails 

 to appear at this time from the posterior side of the transplanted 

 tube, there is httle reason to suppose that such an outgrowth 

 takes place from its anterior side either; for which reason it 

 would seem that the anterior connection is initiated by descend- 

 ing fibers from the anterior stump. 



It is not known to what extent, if any, nerves developing from 

 the transplant participate in this process; but since a certain 

 amount of axial mesoderm was left attached to either side of the 

 transplanted tube, it would seem that such nerves would develop 

 .their usual relations with somite and skin (Coghill, '14), rather 

 than deviate from their ordinary path of development, w^hich 

 would still be open to them, to develop unusual relations with the 

 anterior stump. 



The rapid growth of the brain pushing the anterior stump 

 against the transplant may be an incidental factor in bringing 

 about a union, but complete fusion does not occur until fibers 

 develop. This is illustrated by the results of the G series, in 

 which it was found that connections between transplant and 

 stumps developed in a much shorter time after operation than 

 in the other series. In other words, the formation of a connec- 

 tion between the stump and transplant depends upon the state 

 of development of nerve processes. The location of the connec- 

 tion between the anterior stump and transplant, as seen in 

 figure 18, B, clearly indicates its motor character. 



As regards the connection between the transplant and the 

 posterior stump, everything points to its being initiated by the 

 continued growth backward, through and beyond the transplant 

 of descending fibers from the anterior stump, augmented perhaps 

 by similar fibers from the transplant itself. In the first place, 

 the participation in this process of nerves arising from the trans- 

 plant may be ruled out for reasons already given. In the second 

 place, there is no indication of processes growing forward from 

 the posterior stump even after well developed anterior connec- 

 tions are formed (fig. 7) . While the posterior stump at this time 

 shows every indication of growth and development, its surface 



