BRANCHIURA SOWERBYI BEDDARD. 289 
fibres, elongated, fusiform, with central nucleus, or sometimes branched and star-shaped, 
which traverse the cavity of the branchia from side to side. These fibres are obviously 
the branched cells which I have described above; but I can find no reason to suppose 
that they are muscular, either in Bepparp’s description or my own preparations. On 
the one hand, the observed movements of the gills could not be accounted for by the 
contraction of such fibres; while, on the other hand, all the movements shown by the 
gills in my specimens could be caused by a contraction, on one or other side of the gill, 
or on both sides simultaneously, of the fibres derived from the circular muscular coat. 
A fairly obvious feature in the constitution of the body-wall is the lateral line. It 
exists on each side within the circular muscular layer as an ageregation of cells, which 
in its situation and in its relation to the longitudinal muscular layer recalls the similar 
structure inthe Nematodes. The circular muscular layer is continuous over the line of 
cells, but the longitudinal layer is completely divided by it on each side (figs. 2, 3, 4). 
The cells are of somewhat small size, their outlines indistinct, their nuclei ovoid or spindle- 
shaped. The line extends, midway between dorsal and ventral rows of setee, from the 
third or fourth segment to within a few segments of the posterior end. It is easily 
followed in transverse sections; its nature can also be seen in vertical sections where 
the lateral body-wall is cut tangentially ; the line of cells is seen to form a continuous 
track, of uniform width, in the substance of the longitudinal muscular layer. The line 
is continuous, however, only as far back as the anterior gill-region ; behind this it is 
interrupted, and consists of a series of segmentally arranged groups of cells in the 
posterior part of each segment in front of the septum. Near the posterior end of the 
body the groups of cells, as seen in transverse sections, project further inwards and 
spread out somewhat in the body-cavity (fig. 4). The lateral line is also the situation 
- from which numerous bundles of muscular fibres arise.* 
The celom and its partitions.—The partitions which separate off the cavities in the 
gills, and the question of the ecelomic nature of these latter, have already been considered. 
The septa are extremely thick and muscular in the anterior part of the body (fig. 2). 
The first septum is #; from here onwards to ,° the septa have the above character; +2 
and all succeeding septa are thin; they contain, however, muscular fibres, both radial 
and circular. 
BepparD states that “there appears always to be a partition which shuts off the 
upper part of the ccelom from the lower part” (he is speaking of the branchial region) ; 
the upper cavity he found “exclusively occupied by the intestine, the lower cavity by 
the nervous system and the principal blood-vessels ;” in his figure the partition is shown 
as a thin peritoneal membrane, on which are a number of nuclei. 
I do not find any partition of this nature in my specimens. There are, however, in 
the branchial region a number of well-defined, fairly thick bands, which pass across 
from one lateral line to the other. ‘l'hese do not form a continuous sheet, but have a 
* For the most recent contribution on the subject of the lateral line, v. H. Porntwer, “ Beitriige zur Kenntnis der 
Oligochetenfauna der Gewisser von Graz,” Zeit, f. wiss. Zool., Band xeviii., Heft 4, 1911, 
