450 Prof. M'lntush on ihe 



inferior and external to the ventral longitudinal muscle. 

 The area of the nerve in transverse section is crossed by 

 strong vertical fibres (probably of connective tissue), and the 

 neural canal is external, its compartment being separated by 

 a distinct series of vertical fibres passing from the chitinous 

 support of the ventral longitudinal muscle to the cuticle. 

 Then the canal becomes more closely related to the nerve, 

 while the latter moves under the ventral longitudinal muscle. 

 As soon as the walls of the body are more completely 

 rounded (in section) the neural canal occurs at the outer 

 and inferior border of the nerve-area, which now lies 

 under the raphe to which the vertical and oblique muscles 

 are attached. Thereafter the neural canal glides on each 

 side to the inner and inferior border of the nerve and its 

 calibre is considerably increased. Each then gets wholly 

 below the nerve, the most conspicuous vertical fibrous band 

 being external. Within is a fine chitinous-like membrane, 

 which does not form a very contractile lining, though the 

 action of the fibres around it may assist in this respect. 

 The canal shows no current of Huid in the living form, and all 

 that can be said of it in the preparations is that it sometimes 

 contains a translucent gelatinous substance. The nerves 

 and neural canals preserve the foregoing relations till they 

 reach the region in front of the seventh pair of bristle-bundles, 

 where the canals leave the nerve-trunks, pass inward under 

 the short transverse muscle, and unite in the middle line to 

 form a single large canal, which thus lies between the nerves 

 and separated from them by a considerable hypodermic 

 interval. The extreme shortening of the transverse ventral 

 muscles at the posterior part of the ninth segment permits 

 the approximation of the nerve-cords, so that at the com- 

 mencement of the median ventral blood-vessel they are 

 situated at each side of the large neural canal, and soon (in 

 the same segment) insinuate themselves above it. This 

 arrangement continues to the posterior part of the body, 

 but toward the tip of the tail the nerves form a single 

 (united) cord ; while the neural canal (which in the ordinary 

 sections forms a large transversely flattened channel, like 

 that of a non-contractile vessel) diminishes and disappears. 



A series of fine nerve-branches, forming a plexus, is some- 

 times observed passing out to the lateral organs. The twigs 

 run in a parallel manner at first, then diverge, their fine 

 branches anastomosing in various directions. 



