No. 2.] THE MORPHOLOGY OF DERO VAGA. 169 
As regards the same author’s view that this cell cord repre- 
sents the sympathetic system, I can find no nerves extending 
from the line to the alimentary canal, to the setae, and to the 
nephridial openings, but I do find muscle fibres in these posi- 
tions (Pl. XIV, Fig. 18), and some of them I at first mistook 
for nerves, but later was convinced that they were muscles. 
In my early investigation I thought I had found sense organs 
in this line, but later I found the organs in the epidermis just 
above and below the line. The line of cells also increases in 
width near the setae and at the dissepiment, but this is due to 
a massing of muscles in these regions, and not to the presence 
of sense organs. 
Vejdovsky also states, in describing the large sense organs 
of WV. appendiculata, that the “lateral ganglion cell cords”’ give 
off branches encircling the segments, and that the organs are 
in these bands and are innervated from them, and not from the 
central nervous system.! 
In Dero there is a band of cells somewhat resembling the 
cells of the lateral line which encircles the posterior part of 
each segment (Pl. XIV, Fig. 10), but I have clearly made out 
that the sense organs do not occur in this band, but occur 
before and back of it. Gold chloride does not stain this band, 
and it in all probability is composed of gland cells. 
I do not wish to deny that there are any nervous elements in 
connection with this line, but I do believe that all the elements 
that have heretofore been considered nervous are not of that 
character, and this being the case it certainly bears no relation 
to the lateral-line system of vertebrates. 
IV. THEORETICAL CONSIDERATIONS. 
I. ORIGIN OF METAMERISM. 
The facts above presented have a very important bearing in 
support of the colonial theory of the origin of metamerism. 
Stated briefly, this theory proposes to account for the origin 
of segmentation in animals by supposing that they arose from un- 
segmented forms through the process of multiplication by fission. 
1 Vejdovsky, /.c., p. 97. 
