182 G. E. COGHILL 



nature of the terminals. The section from which this figure is 

 taken passes between the sixth and seventh myotomes of an 

 embryo of the coiled-reaction stage. The fiber here represented 

 passes latero-dorsad from the border of the cord to a mesenchyme 

 cell, where it branches and sends one division directly against the 

 end of the myotome. At the end of the fiber it sends out claw- 

 like processes into the myotome. But the most striking part 

 of the structure is the series of spinous projections which beset 

 the fiber through the last part of its course. These processes 

 are clearly continuous with the substance of the fiber itself, and, 

 by shifting the focal plane, one can clearly determine that they 

 project outward from the fiber and upward in the preparation 

 towards the observer. In this way they can be traced out into 

 fibrillar structures that reach the limits of vision with ordinary 

 oil immersion lens systems. To complete the picture, however, 

 one must appreciate that the adjacent section of the series shows 

 that the myotome, seen here only in contact with the end of the 

 fiber, is shifted over the position of this fiber; so that these pro- 

 jections are clearly seen to be the terminal arrangement of the fiber 

 upon the surface of the myotome. The spines along the border 

 of the fiber are of the same sort as those at the end, but have been 

 lifted away from their normal relation with the myotome. This 

 preparation completes the picture of such conditions as are par- 

 tially shown in figures 7, 10, 11, 12, 13 and 14. 



The intimate contact between the spinal cord and the myotomes 

 has already been mentioned. This relation is seen in its most 

 complicated form in the caudal region of embryos of the non- 

 motile stage, and is pictured in figure 22. This section is from 

 a horizontal series but, with reference to the spinal cord in this 

 region, it is directed obliquely from dorsad, cephalad and ventrad. 

 The relation between the spinal cord and the myotome is here 

 essentially the same as that figured between the skin and the 

 cord in figure 19, only it is even more extensive. In many regions 

 of this contact there is no perceptible border line between the 

 cord and the myotome and the structures of one seem to pass 

 over among those of the other and become indistinguishable 

 from them. In the most dorsal portion of the area of adhesion is 



