OLIGOCHATA OF TROPICAL EASTERN AFRICA. 209 
two atria the lumen of each gets to be more and more oval in 
outline. As in other species of the genus Eudriloides, the 
aperture of the atria is furnished with penial sete; there are 
two of these, one on each side; the penial seta is curved into 
an §-shape; the curvature is much more pronounced than that 
of the ordinary set; the free tip of the seta appears to be 
bifid ; it is ornamented with a series of minute denticulations ; 
these occupy a restricted area just in front of the actual tip of 
the seta; their shape can be understood by an inspection of 
the accompanying figure (fig. 20). 
There is in connection with the male efferent apparatus a 
very complicated arrangement of muscles, recalling in many 
particulars the corresponding structures in Eudriloides 
brunneus. These structures are best elucidated in glycerine 
preparations of the worm from which the alimentary tract has 
been removed. In such a preparation the two penial setz will 
be seen on either side of the male pore lying somewhat 
obliquely ; near to the distal end of each seta a strong bundle 
of muscles is attached ; the actual attachment is not extensive, 
but the muscles rapidly fan out, and where they are inserted 
on to the body-wall form a bundle of considerable dimensions. 
The muscular fibres forming these two bundles are bound up 
into separate muscles, as is shown in the figure illustrating 
this copulatory apparatus (fig. 18). On the opposite side 
of each seta there is another strip of muscles which runs 
obliquely almost in the same straight line as the first mentioned 
set; this bundle of muscles is, however, of equal diameter 
throughout, and is not nearly so wide as the first. It seems 
clear that these two sets of muscles have an opposite effect, 
moving the penial seta in different directions. We now come 
to the muscles of the bursa copulatrix. The two atria join to 
form a tube, which is much narrower than either of themselves ; 
this unpaired tube is covered by a layer of muscles which runs 
transversely across the body, being attached to the body-wall 
in the immediate neighbourhood of the penial seta on each 
side. From the same point of origin arise a few fibres which 
are inserted upon the tube itself, and a still more slender 
