482 F. W. GAMBLE AND J. H. ASHWORTH. 



The nucleus is placed near the broader end of the cell, while 

 from the narrow end the single process arises, and within 

 this a few stout neuro-fibrillae can often be seen pursuing a 

 characteristically sinnous course into the fibrous part of the 

 cord. The smaller ganglion cells are placed more laterally. 

 Their shape is very difficult to determine, and we are not 

 sure whether they possess more than one process. The 

 nucleus measures *004 mm., and has a well-marked chromatin 

 network with a very small nucleolus. 



Fibrous Part of the Nerve cord. — Except in the 

 dorsal region under the giant-fibres, the two fibrous tracts 

 of the cord are separated by a vertical sheet of neuroglial 

 tissue embedded in a transparent matrix. In ti-ans verse 

 section they do not present the same appearance in all 

 regions nor in all pai-ts of a segment. Posteriorly they are 

 much more extensively invaded by branched processes of the 

 neurilemma, which is only slightly developed in the branchial 

 region ; and at the origin of the spinal nerves the processes 

 of the two central masses of ganglion cells give the section 

 at this point a more strongly fibrous aspect than in the 

 intei-mediate zones. 



The methods we have chiefly employed are not adapted 

 for a successful study of the difficult subject of neuropile. 

 Yet we may say that the characteristic appearance of this 

 tissue is almost absent from the nerve-cord, while it is well 

 shown in the brain. The nerve-fibres themselves, though 

 surrounded by an intricate neuroglia investment, do not stain, 

 or at most show faint indications of fibrillas. 



Spinal Nerves.' — A pair of nerves arise from the cord 

 opposite each interannular groove, along which they run 

 upwards and supply the body-wall. Opposite each chasti- 

 gerous annnlus, however, there are from two to four pairs of 

 nerves. Each nerve consists of a stout band of fibres which 

 pierces the ganglionic layer at the outer angles of the cord, 

 and then runs outwards between the circular and longitudinal 

 layers of muscle, each of which it supplies. In several cases 

 » See PI. 29,11^.78. 



