60 NERVOUS SYSTEMS AND SENSE ORGANS 



cells found on the dorsal side of this tract. They are most abundant 

 at its ventro-lateral angles. 



On each side of the median tract are three not sharply marked 

 portions; (a) a dorsal tract mostly of deep staining fibers, (b) a 

 latero-ventral tract bounded by a layer of clear cells, a tract 

 mainly made up of longitudinal dark fibers, (c) a medio-ventral 

 tract larger than the last and between it and the median. It con- 

 tains dark fibers running in all directions but mainly longitudinally 

 and also clear fibers. 



The nerve cells send their fibers in radially. The "Punktsub- 

 stanz" is composed of fibers from two kinds of nerve cells. 



The nerve cord has no neural sheath but is immediately sur- 

 rounded by a small-celled parenchyma. Outside of the outer nerve 

 cells of the cord is a sheet of dark staining fibers. 



At intervals along the nerve cord are transverse commissures 

 of fibers extending from the dorso-lateral angle of one side to that 

 of the other. There is no segmental grouping of the nerve cells. 

 The transverse commissures also are not metameric as they are too 

 irregular and too close together. 



The so-called cephalic ganglion is a slightly enlarged anterior 

 end of the nerve cord. It is more thickened from side to side than 

 dorso-ventrally. The nerve cells are numerous but limited to the 

 median line. In the head the fiber tracts appear like a large median 

 one each side of the middle line. Thei'e is a transverse commis- 

 sure near where the cephalic nerves meet. As this is on the ventral 

 side it has been called the ventral commissure. According to Mont- 

 gomery there is no brain or supra-oesophageal ganglion. 



The cloacal ganglion of the female is the enlarged posterior 

 end of the ventral nerve cord just anterior to the point where the 

 lateral lobes branch. From the ganglion there are anterior and 

 posterior cloacal nerves. 



The cloacal ganglion in the males is not so sharply limited as in 

 the female. The length of the ganglion varies in different indi- 

 viduals of the same size. Small nerves pass to the vasa deferentia. 

 The ganglion divides into a right and left caudal nerve into the 

 caudal lobes. 



In both sexes the neural lamella attach the nerve cord to the 

 hypodermis. It is it.self of hypodermal natui'e. At the point of 

 the attachment of the neural lamella, the hypodermis is conical on 

 cross section. There is a clear area here in which the longitudinal 

 hypodermal nerve is located. It is composed of nerve fibers from 

 dark nerve cells of the ventral cord. This hypodermal nerve runs 

 as far as the central nervous system. 



Fibers enter the hypodermis by way of the neural lamella 

 apparently from cells in a ventral position. Upon entering the 



