No. 3-] NERVOUS SYSTEM OF CYNTHIA PARTITA. 105 



Structure of the cell process is here plainly seen, as well as the 

 characteristic wavy course of the fibrils. The fibrils do not 

 form an entrance cone, but seem to spread out in the cell-body, 

 especially toward the periphery. In the axis cylinder the fibrils 

 appear to hold an irregular course, and do not run absolutely 

 parallel. These fibrils are separated from each other by a 

 homogeneous substance which does not stain with haematoxylin, 

 and but slightly with eosin or erythrosin. This is the peri- 

 fibrillar substance, probably the hyloplasm of authors. The 

 structure of the sheath is very difficult to make out ; it 

 appears to be almost homogeneous or very finely fibrillar, as 

 described by Apathy and Bethe. No myelin substance could 

 be proved. In the nerve trunks the individual processes can 

 rarely be differentiated in longitudinal section, and then only in 

 very small, loosely con- 



structed nerves, such as 

 are found in the dorsal 

 lamina. But in cross- 

 section the structure is 

 much easier to make 

 out. If sections be 

 soaked for twelve hours 



./.__ 



- m. c. 



Fig. 4. — Cross-section of nerve trunk in dorsal lamina, show- 



in the irOn-alum SOlu- Ing fibrils and sheaths. Adult specimen. «/, nerve fibrils; 

 tion and fortV - eis'ht w-^-. muscle fibrils in cross-section. Von Rath. Haema- 

 _ toxylin. Camera drawing. {5 x oc. 6 (Zeiss). 



hours or more in the 



haematoxylin solution, then the stain is only slightly drawn 

 out, so that the section looks black, a very good idea of the 

 nerve trunk can be obtained. Fig. 4 shows such a specimen. 

 The nerve trunk is usually free from any connective-tissue 

 envelop and is found lying free in the connective-tissue space 

 (mesenchyme). The sheath of the cell process stains a dull 

 blue or blue black, while the fibrils take a deep black. These 

 fibrils may be united into a little group inside the sheath (when 

 a sheath is present) or scattered indifferently through the 

 perifibrillar substance. Often they are found concentrically 

 arranged just inside the sheath. Sometimes only one or two 

 large fibrils are found. 



It seems probable that one of these stages merges into 



