No. 2.] THE MORPHOLOGY OF DERO VAGA. 167 
(1) In most, if not in all, Oligochaetes there exists on either 
side of the body in the lateral line a row of peculiar cells 
extending the entire length of the worm. 
(2) Sense organs may occur in or near this line. 
(3) In some forms this cell cord apparently merges into the 
brain. 
(4) In case of multiplication by fission a proliferation of cells 
either in or near this line takes place. 
As to the probable significance of this cell cord the following 
views have been advanced: 
(1) It is a homologue of the lateral-line system of the lower 
vertebrates (Semper). 
(2) It is a part of a sympathetic nervous system (Vejdovsky). 
(3) It is a problematic cell cord of doubtful significance 
(Eisig). 
(4) It is an aggregation of the nucleated plasma parts of the 
circular muscle cells (Hesse). 
(b) Descriptive. 
’ 
The “lateral line” in Devo vaga was noted at the beginning 
of my work on that form, and I have made a careful study of 
it in order to determine its true nature. Starting with the 
idea that we have here a cord of cells which may be compared 
to the “ Anlage”’ of the lateral-line system of lower vertebrates, 
I have been led to accept the view advanced by Hesse, and am 
now confident that it cannot be interpreted as a nervous struc- 
ture. In this form the “lateral line”’ occupies the break 
between the dorsal and ventral half of the lateral muscle areas 
and extends from the head segment to the growing zone at the 
tail, where it increases in width and is lost in the embryonic 
tissue present in that region. The parts of the cells which 
are clearly visible are elongate pear-shaped and extend horizon- 
tally into the coelom, forming a strand composed of two or 
three rows of nuclei. Pl. XIV, Fig. 18, shows the cells as 
they appear in a thick (15 w) cross-section of the worm. The 
nerve given off from the ventral cord is the fourth lateral. 
The muscles extending from the vicinity of the strand to the 
