50 Journal of Comparative Neurology. 



tive body really consists of two parts — an ovoid part embedded 

 in the protoplasm of the peripheral process and continuous with 

 a somewhat wedge-shaped block which extends quite to the 

 central tube. (Text-figure 4). It is therefore clear that the 

 spiral band is really not a separate structure, but is formed of 



Text-figure 4. Lateral views of the tips of two peripheral processes in a 

 spiral organ, a shows a refractive block with a ridge on its upper surface ; b 

 shows one which lacks this ridge and thus builds a smooth turn of the spinal, 



b. r. refractive body; pr. per. peripheral process ; t. cen. central tube. 



the wedge-shaped blocks of the refractive bodies, arranged side 

 by side in a spiral manner around the central tube. One of 

 these blocks has usually seven surfaces. (Text-fig. 4, a, and 

 PI. II, Fig. 46). The two lateral surfaces are closely joined to 

 the corresponding surfaces of adjacent blocks. In living mate- 

 rial this plane of union is not visible ; under the influence of 

 reagents the blocks separate a little from one another and the 

 component parts of the spiral band may then be seen. (Plate 

 II, Fig. 41). The outer surface of each block is continuous 

 with the ovoid part of the refractive body and with the proto- 

 plasm surrounding the latter. The lower surface is free and 

 forms the lower surface of the spiral band ; the upper surface 

 is also free and usually bears an angular ridge which gives the 

 cog-like appearance previously described upon the outer surface 

 of the spiral. The inner surface of one of these blocks usually 

 consists of two parts ; the lower part is concave from side to 

 side and closely joined to the central tube while the upper is 

 free and forms an acute angle with the tube. It is these free 

 upper parts of the inner surface that form the upper border of 

 the spiral band. Sometimes the entire inner surface of several 

 blocks joins the central tube and then the angular ridges on the 

 upper surfaces are lacking. (Text-figure 4, b), and the part of 

 the spiral band formed by these blocks appears smooth. In 



