OF THE NEMATOIDS, PAEASITIC AND FREE. 569 



median lines. No such processes exist anterior to the nervous ring, and those proceeding 

 to it, according to Schneider, together constitute a strong sheath in which are inclosed 

 the real nerve-fibres. According to him, what is actually seen when the band crossing 

 the anterior part of the preparation, made in the manner stated, is examined, is this 

 fibrous sheath, which effectually conceals the real nerve-elements within it. I quite 

 agree with Schneider in this view ; for when the flat surface of the band is examined in 

 this manner, no ganglion-cells or unmistakeable nerve-fibres can be detected in it, 

 though the former elements may be easily recognized in well-made transverse sections, 

 and the real nei-ve-fibres, according to Schneider, may be isolated by dissecting the ring 

 after it has been boiled in dilute nitric acid. 



In connexion with the ring, posteriorly, between it and the arch of the water-vascular 

 system, are many most distinct ganglion-cells with issuing fibres, which are by no means 

 easy of detection, since they are imbedded either in the lateral bands or amongst a web 

 of most delicate fibres and interspersed granules, partly derived from the same lateral 

 bands, and partly from the subjacent muscles. This is the case also with the nerves and 

 cells anterior to the oesophageal ring. Some of the hindermost cells are, doubtless, 

 obscured by the vascular arch, though I have never been able to ascertain that any 

 existed posterior to this. The ganglion-cells behind the ring are arranged into four 

 groups ; two larger (d, d) occupying the substance of the lateral bands, and two smaller 

 (c, c) diverging from a ganglionic mass in the mid-ventral region in connexion with the 

 oesophageal ring. These ventral ganglion-ccUs appear to me to send a few fibres in a 

 curved direction towai-ds the cells in the lateral tracts, though the majority pass forwards 

 to the oesophageal ring and median ganglion. It is from the cells in the lateral tracts 

 that I have principally distinguished the issuing fibres ; they may be distinctly seen as 

 broad bands* directly continuous with the body of the cell, which contains a bright 

 nucleus as well as a small quantity of fine granular matter. To ascertain the relative 

 proportions, I measured these various parts in the cell marked r, and found them to be 

 as follows : — diameter of cell 3^", of nucleus 3x3^", and of fibre at slight distance from 



^"^^^ 3333 • 



In front of the oesophageal ring I could not find so many ganglion-cells existing in 



Ascaris lumbricoides as seem to be present in A. megalocephala, although in both species 

 they are more abundant behind than in front of the ring. The most striking portions 

 of the nervous system anterior to the ring are six great muscular bundles, which pro- 

 ceed forward to the mouth and cephalic lobes. The two bundles containing the largest 

 number of fibres are contained in the substance of the lateral bands {g, g), nervi laterales 

 of Schneider ; whilst those which present the largest and most well-marked fibres are 

 two bundles {/,/), which have been named by the same anatomist no'vi suhmediani, 

 situated on the ventral surface, on either side of the median line and about midway 

 between it and the lateral bands ; these have a serpentine course, and appear to go to the 

 contiguous portions of the two under cephalic lobes. They seem to arise each by two 

 * According to ScmrEiDEB, in transverse section they present a flattened oval appearance. 

 MDCCCLXVl. 4 K 



