An American Earth irorm of the Family Phreorycttdc'. Ill . 



Ganglion cells are but few on the upper half of the cord, but 

 are almost continuously distributed on the under surface except 

 at the dissepiments, where the cord is rapidly reduced in si/e 

 and contains no ganglion cells. There is nothing in the nerve 

 cord or its delicate sheath to represent the giant fibers of the 

 earthworm. 



The ventral cord is supported beneath, at the center of each 

 somite, between the ganglionic swellings, by the " ventral or- 

 gans " of Timm (PI. VI., Fig. 5, & PI. VII., Figs. 6 & 7),*— pyra- 

 midal pads or cushions of cells, the outer ones large, distinct, 

 nucleated, the inner resembling the ganglion cells of the nerve 

 cord itself. The apex of the pyramid extends between the longi- 

 tudinal muscle bands, and the base of it commonly supports the 

 cord, the lateral angles frequently extending upwards, beside 

 the cord, and sometimes, especially in the anterior somites, 

 half surrounding it (PI. VII., Fig. 6). In the posterior part 

 of the body, however, the cord and the ventral organs are 

 much less closely connected, and often lie side by side quite free 

 from one another. These cellular masses are longest from 

 before backwards, and are connected with each other by a 

 single nerve fiber running from one to the other, this having 

 occasionally a nucleated cell in its course. 



The lateral nerves ( PI. VI., Fig. 5 ) all pass from their 

 origin outwards and downwards through the longitudinal mus- 

 cular layer of the body wall to the circular muscle, beneath 

 which they are distributed. They are swollen and slightly gan- 

 glionated just beyond their origin. Three pairs of these lateral 

 nerves rise in each somite (excepting a few of the most ante- 

 rior), two from the posterior swelling of the ganglion and one 

 from the anterior. The posterior pair arise immediately in 

 front of the dissepiment, the second pair a short distance fur- 

 ther forward, — commonly immediately behind the ventral 

 organ, — and the first pair (which pass directly downward) at 

 about the anterior fourth of the somite. These nerves are given 

 off on the same horizontal plane, and the pairs are opposite. 



* The structure of these bodies, as well as their greater size in the 

 anterior segments, seems to me to bear out the suggestion of Tiram 

 that tliey are sensory organs. 



