THE NERVOUS SYSTEM OF AMPHIBIA 183 



found a giant ganglion cell which sends its process out into one 

 of these fused region. In other words, this ganglion cell holds 

 the same relation to the myotome as does that of figure 21 to 

 the skin. Figures 21 and 22 are taken from the region of the 

 unsegmented mesoderm of the same embryo. 



In conclusion upon this phase of the work it may be confidently 

 stated that the giant ganglion cells are muscle-sensory as well as 

 skin-sensory in function. In fact the study as a whole gives me 

 the impression that the muscle-sensory elements are more highly 

 differentiated in the youngest stage studied than are the skin- 

 sensory elements, but of course there is no means of determining 

 this mathematically. In the youngest stage of this series both 

 systems are established in their terminal relations with the periph- 

 eral organs. 



(3) The innervation of both skin and muscle by the same neurone. 

 Since the neurones of the sensory column innervate both muscu- 

 lar and cutaneous organs a question arises concerning the possibil- 

 ity of differentiating two sets of neurones in the system, the one 

 innervating the skin and the other supplying the muscular sys- 

 tem. The proposition of undertaking to make such an analysis of 

 the system, however, is met with the unmistakable evidence that a 

 single cell of this group, in many cases, terminates both in a 

 myotome and in the skin. Several figures have been made to 

 illustrate this relation. 



Figure 2 is taken from the section adjacent to that of figure 1, 

 and shows the continuation of the fiber, which has terminals in 

 the myotome in figure 1, on out to the skin. Figure 6, in Uke 

 manner, is from the section adjacent to that of figure 5. A com- 

 posite of the two figures would give unmistakable evidence of 

 one fiber branching and sending one process to the skin and the 

 other to a myotome. In figure 9 this relation appears in one 

 and the same section. Here the branching occurs near the skin 

 and the branch that goes to the myotome has the characteristic 

 ending described above in connection with specific treatment of 

 the relations with the myotomes. Figure 8 is from the section 

 adjacent to that of figure 9 and shows another branch of the 

 same neurone terminating in the skin. The fiber of figures 15, 



