TRANSPLANTING NEURAL TUBE OF AMBLYSTOMA 179 



could be obtained of conduction through the transplant. By 

 this time the bend in the axis had become extremely acute 

 (fig. 17, A) 



Sections showed that the loss in conductivity was due to the 

 formation of a cartilaginous partition cutting through the neural 

 axis just behind the transplant. Figure 17, B, a section in the 

 medial plane, passes through the thinnest part of the partition 

 and shows the transplant firmly united in front with the brain. 

 In all probability the transplant completed its anterior connec- 

 tion, but was unsuccessful in developing a posterior connection 

 of sufficient stability to resist the pressure of the growing posterior 

 wall of the brain capsule, with the result that a foramen magnum 

 failed to develop, and the brain became completely hemmed 

 off anteriorl}^ 



III 



In the F series of embryos the operation was made in the 

 region of the fifth and sixth somites, and the results of these 

 experiments are somewhat different from those of the other 

 series. All were operated the same day, April 16th, and none of 

 them during thirty days following the operation showed any 

 evidence, by the method of tactile stimulation, of nervous con- 

 tinuity through the transplant. The operating stage is shown in 

 figure 1, C. 



Let us consider a few examples. F7, killed May 7th, twenty- 

 one days after the operation, showed in sections that the trans- 

 planted tube was widely separated from the stumps of the brain 

 and cord by muscle that had developed from transplanted 

 somites. The transplanted tube had, however, undergone a 

 certain amount of growth and differentiation, and showed no 

 signs of atrophy. Practicall}^ the same conditions were found 

 in Fl, killed ]May 17th, ten days later than F7. F3, killed 

 ]\Iay 18th, one day after Fl, displaj^ed in sections the same wide 

 separation between the transplant and the stumps, but in this 

 case the transplant gave every appearance of atrophy in its 

 reduced size and ragged form. Had the embryo been allowed to 

 live, the possibility of its establishing connections between the 



