No. 2.] THE MORPHOLOGY OF DERO VAGA. 153 
which it is constantly being formed. I have observed no 
specimens in which this connection did not exist. Sexually 
developed forms as well as those undergoing fission were 
observed. In consequence of this continued growth the ganglia 
vary in number. 
A cross section of the ventral cord through the widest part 
is shown highly magnified in Pl. XIV, Fig. 17. The nerves 
emerging from the cord (/.z.) are those which pass through the 
setae bundles. The ganglion cells (g.c.) are arranged in three 
groups, two lateral and one ventral. The fibrous portion (/2.) 
is divided by faint clear spaces into three parts. In the lower 
portion of the middle part, the cross section of the intermediary 
nerve (z.z.) may be seen, and in the dorsal part of the fibrous 
portion are three giant fibres (gf). Two muscle bands (#us.) 
appear, one on either side of the fibrous bundle, and a blood 
vessel (d.v.) lies closely applied to the dorsal surface of the cord. 
The examination of dissected specimens shows large irregular 
cells scattered along the dorsal surface of the cord. In the tail 
region and at a fission zone these cells are very much more 
abundant. Without doubt they correspond to the “ chorda 
cells’ of Semper,! and are probably identical with the “ neo- 
blasts” described by Miss Randolph? in Lumbriculus. 
In describing the lateral nerves I shall begin with the simpler 
condition found in the body segments, and proceed later to 
describe the nerves in the so-called “head.” 
As has been mentioned before, each segment of the body 
contains a ganglionic swelling of the ventral cord. This gan- 
glion reaches its maximum width at a point posterior to the 
middle of the segment, and a portion of the swelling extends 
through the dissepiment into the next following segment. Four 
pairs of lateral nerves are given off from each ganglion (Pl. XIII, 
Figs. 3, 6). These nerves pursue essentially the same course. 
On leaving the cord they pass obliquely downward and away 
from the cord, and pass through the longitudinal muscle layer 
1C. Semper, Die Verwandtschaftsbeziehungen der gegliederten Thiere, III, 
Strobilation und Segmentation, Avéeit. a. d. Zool.-Zoot. Inst. Wiirzburg, Bd. III, 
1876, p. 186. 
? Harriet Randolph, The Regeneration of the Tail in Lumbriculus, Journ. of 
Morph., Vol. VII, 1892. 
