1007.] NATURAL SCIEXCES OF I'lll LA DKLl'lI I A. 105 



cells. As the two coininissures reach the anterior border of the inoutli 

 they are reunited In- a ))undle of nerve fibres, the preoral transverse 

 connnissure (figs. 1 and 20, pr.com.). This is of uniform diameter 

 throughout, and about one-thirtl of that of the circumoesophageal 

 commissures at this point. It lies partially embedded in the anterior 

 wall of the oesophagus, just above the point where the latter meets the 

 h}'p()tlermis of the ventral portion of the head, as is shown in fig. 23. 

 Accompanying it, on its inner side, next to the oesophageal wall, are a 

 few muscle fibres which terminate on either side in the body wall. 

 In the series from which fig. 1 was taken, a series remarkably favorable 

 for the study of the nervous system, clear evidences were found of 

 nerve fibres which were given off to the inner surfaces of the hypodermal 

 cells from the circumcesophageal commissures, at a point opposite to 

 that of the junction of each with the preoral commissure. These nerve 

 fibres have the appearance of being, to some extent at least, continu- 

 ous with those of the preoral commissures. Moreover, a ganglion 

 cell was found on each side, laterad of the junction of the preoral 

 and circumoesophageal commissures, and having the appearance of 

 belonging to the fibres just mentioned (see fig. 1). 



Just posterior to its union with the preoral commissure, each cir- 

 cumoesophageal commissure gives off a large branch, the oesophageal 

 nerve (figs. 1 and 3, oes.n.). This nerve at first runs in a dorso-pos- 

 terior direction, following the oesophagus, and meeting in its course the 

 ducts of the salivary glands (s.g.d.). It then accompanies these back- 

 ward, but, before reaching the glands themselves, in the middle of the 

 first trunk segment, it suddenly disappears. It possesses a large 

 calibre throughout its course, and is elliptical or flattened in section, 

 being closely applied to the outside of the oesophageal w^all. Near 

 its point of origin it is surrounded by a few ganglion cells, but these do 

 not follow it but a very short distance (fig. 1). 



After giving off the oesophageal nerve the commissures pass back- 

 ward around the oesophagus, just below the lateral longitudinal mus- 

 cles, and are now completely embedded in the hypodermis, just outside 

 of the line of junction of the latter with the oesophageal wall (figs. 3 

 and 4). In section their form has changed from round to long-elliptical ; 

 this alteration being correlated with a decrease in the thickness of the 

 hypodermis. The commissures are now so completely incorporated 

 with the hypodermis that they can only be distinguished by their 

 staining reaction and, to a limited extent, by their histological struc- 

 ture. At the posterior border of the mouth each circumoesophageal 

 commissure, in tlie example from which fig. 1 was made, exhibits an 



