230 PROFESSOR F. JI. BALFOUR. 



out and comes to an end, while the commissures pass imme- 

 diately below the wall of tlie pharynx (PI. XVI, figs. 14, 15). 

 The ventral cords themselves at first approach very close to 

 each other in this region, separating again^ however, to en- 

 velope between them the pharynx (PI. XVIII, fig. 22). 



There are eleven commissures in front of the first pair of legs 

 (PI. XVIII, fig. 22). The three foremost of these are very close 

 together, the middle one arising in a more ventral position 

 than the other two, and joining in the median ventral line a 

 peculiar mass of cells placed in contact with the oral epithelium 

 (fig. 14). It is probably an organ of special sense. 



The ventral cords give off a series of nerves from their outer 

 borders, which present throughout the trunk a fairly regular 

 arrangement. From each ganglion two large nerves (figs. 8, 

 22, 26) are given off, which, diverging somewhat from each 

 other, pass into the feet, and, giving off branches on their way, 

 may be traced for a considerable distance within the feet along 

 their anterior and posterior borders. 



In front of each of the pair of pedal nerves a fairly large 

 nerve may be seen passing outwards towards the side of the 

 body (fig. 22). In addition to this nerve there are a number 

 of smaller nerves passing off from the main trunk, which do 

 not appear to be quite constant in number, but which are 

 usually about seven or eight. Similar nerves to those behind 

 are given off from the region in front of the first pair of legs, 

 while at the point where the two ventral cords pass into the 

 oesophageal commissures two large nerves (fig. 22), similar to 

 the pairs of pedal nerves, take their origin. These nerves may 

 be traced forwards into the oral papilla?, and are therefore to 

 be regarded as the nerves of these appendages. On the ventral 

 side of the cords, where they approach most closely, between 

 the oral papillae and the first pair of legs, a number of small 

 nerves are given off to the skin, Avhose distribution appears 

 to be to the same region of the skin as that of the branches 

 from the commissures behind the first pair of legs. 



From the oesophageal commissures, close to their junction 

 with the supra-oesophageal ganglia, a nerve arises on each side 



