568 THE AMERICAN NATURALIST. [Vor. XXXV. 
Immediately above the abnormal nerve cord (cd.n.') is an 
extra ventral blood vessel (Fig. 2, va.v.'). Beginning in the 
second interpolated somite, it can be traced back through the 
twelve succeeding metameres.  Anteriorly it is connected by 
branches with the normal dorsal and ventral blood vessels and 
gives off ramifications to the organs of the interpolated region. 
Posteriorly there is no such direct communication with the 
normal blood vessels, and twigs from the normal vessels sup- 
ply a portion of the blood to the extra parts in this region. In 
the last seven or eight abnormal somites this ventral vessel 
is absent and the interpolated parts receive their entire blood 
supply through small branches from the normal vessels. In 
each somite throughout the abnormal region a large branch 
of the dorsal blood vessel runs around the /eff side of the 
intestine directly to parapodium s., passing the interpolated 
parts. As its main trunk enters this appendage it gives off a 
good-sized twig to Zx.' — Parapodium dr.’ thus receives a better 
(double) supply of blood than s.', and Figs. 3 and 4 show that 
dx.' is also better developed than s.’ 
The abnormal nerve cord (Fig. 2, cd.z.') shows several inter- 
esting peculiarities. It has no direct connection with the 
main nerve cord, and it is normally situated with reference 
to the interpolated parts, lying between the two supernumerary 
longitudinal muscles. Its ante- 
rior end is found in the second 
abnormal metamere, whence it 
can be traced back through fifteen 
somites. Like the normal cord, 
it is supported by a network of 
neuroglia tissue, the whole being 
enclosed in a fibrous neurilemma 
sheath, which is thicker at the 
anterior than at the posterior end. 
A transverse section through this 
cord in the region of the third 
abnormal metamere exhibits the 
conditions shown in Fig. 5. There are eight small masses 
neuropil, surrounded ventrally and laterally by groups of large 
salis up in the figure.) (x 6o. 
