184 « G. E. COGHILL 



16 and 17, taken from successive sections also has the appearance 

 of innervating the myotome at its base where it leaves the cord 

 in figm-e 15, while it sends terminals to the skin in figure 17. In 

 figure 23 there is a clear case of a large fiber from a giant ganglion 

 cell sending a branch directly into the myotome, as it passes 

 across the ends of the cells, and continuing on out to the skin. 

 In figure 25 the giant ganglion cell fiber can be seen to pass 

 through a groove in the end of the myotome and from this posi- 

 tion to send a characteristic spinous process in among the cells 

 of the myotome. The fiber in its further course branches out to 

 the skin. 



{Jf) The number of peripheral fibers. No special attempt has 

 been made to count the number of peripheral fibers in the giant 

 ganglion cell system, but some data on this point, extracted from 

 my records of the general study, may be of interest. 



The total number of fibers that were noted as adapted to special 

 study and for written records was 186 in the thirteen embryos 

 of the non-motile stage, and the largest number for any one 

 specimen was 50. -For seventeen embryos of the early-flexure 

 stage the corresponding numbers are 185 and 57. In fourteen 

 embryos of the coiled-reaction stage the total is 87 and the maxi- 

 mum in a single specimen, 28. For ten specimens of the swim- 

 ming stage, the numbers are 115 and 36. 



Further examination of my notes on the study of the giant 

 ganglion cells and their fibers shows that of the 186 peripheral 

 fibers studied specially in the non-motile embryos, and of the 185 

 studied specially in the embryos of the non-flexure stages, 136 

 in each case pass out over or in near relation to the ends of the 

 myotomes. In the non-motile embryos, according to my judg- 

 ment in studying from section to section 38 fibers were traced 

 to the skin, 34 were regarded as terminating in the myotomes, and 

 20 had the appearance of ending both in the skin and in the myo- 

 tomes. In the earlier embryos practically all the fibers observed 

 had intimate relation to the ends of the myotome. In the older 

 embryos occasional fibers, particularly in the more rostral regions, 

 were observed to pass out du-ectly to the skin over the middle 

 part of myotomes. 



