ROUND WORMS 59 



Ward, 1892, on Nectonema, a pelagic marine form, gives an 

 account of the nervous system. The anterior ganglionic mass or 

 brain forms a large portion of the floor of the anterior chamber. 

 The oesophagus lies in a groove in its center. There is but a slight 

 dorsal commissure above the oesophagus. The ganglion cells are 

 not abundant in the brain. A smaller kind is more abundant than 

 another sort which is very much larger. There are five pairs of 

 these last which are nearly constant in position and form. The 

 ventral nerve cord continues from the brain and runs the length of 

 the body separated into three areas to correspond to the three nerves 

 of which it is composed. Some large cells in the cord are much like 

 those in the brain. In the male the ventral cord is much enlarged, 

 being larger than the brain itself. In the female the anal ganglion 

 is but slightly larger than the central cord with which it is 

 connected. 



Camerano, 1897, considers the nervous system to consist of a 

 supraoesophegeal ganglion and a ventral nerve strand. Mont- 

 gomery, 1903, finds a ventral unpaired nei've trunk with the cephalic 

 ganglion at its anterior enlargement and the caudal or cloacal 

 ganglion, a posterior enlargement. To the peripheral nervous 

 system belong the neural lamella; the endings in the hypodermis of 

 the fibers of nerve cells situated in the central nervous system ; the 

 hypodermal longitudinal nerve; sensory cells in hypodermis; non- 

 sensory hypodermal nerve cells and the nerve fibers which innervate 

 the cloaca of the female and the vasa defi"erentia of the male. Two 

 types of cells were found in the nerve cord. One type contained but 

 little chromatin. These cells on the lateral sides of the cord are 

 quite uniform and small. On the ventral side there are smaller and 

 larger cells of this type. The larger or giant cells are less numer- 

 ous. Sometimes there is a paired arrangement of these cells but 

 usually they are irregularly placed one behind another. These 

 cells seem to be bipolar with two large processes proceeding from 

 the cell directed towards the fibrous core of the nerve cord. Some 

 of the small cells appear to be bipolar or multipolar. All cells are 

 without membranes. Montgomery thinks that these deeply staining 

 cells are probably motor and visceral in function. 



The deeply staining cells seem to be multipolar with very long 

 nrocesses. It could not be determined whether there was anas- 

 tomosis of the processes. These cells seem like the multipolar 

 neuroglia cells of other invertebrates but processes pass into the 

 hypodermis. 



The ventral cord seems to be made up of three converging rays 

 of fibers but each lateral ray is made up of several distinct fiber 

 tracts. The median tract is the largest and is made up of longi- 

 tudinal fibers which are closely arranged. Very rarely are nerve 



