PACIFIC COAST OLIGOCH MTA. 65 
Body-wall. The various layers offer nothing of great interest. The longitud- 
inal muscular layer is slightly thicker at the dorsal part, and so is the part situated 
between the 3d and 4th sete. ‘The muscles in this layer do not show any feathery 
arrangement around a central fiber, but are irregularly distributed. There are no 
dorsal pores. The body-wall in somites xi and xii is thinner than the anterior somites. 
Areciform muscles. The inner surface of the body-wall in somites xyii and 
xviii, and partially also in xvi, are covered with numerous arciform muscles which 
stretch transversely or diagonally across the body cavity, connecting the region run- 
ning through the outer couple of setee with that of the male pore and the inner setze. 
The number of muscular bands in these somites is very great and they vary in length 
and thickness. There is also a slight variation in different specimens, the main fasci- 
cles being, however, always in the main the same. These muscles are best viewed 
when seen from above, the body wall being spread open and the sacculated intestine 
removed. As will be seen from the drawing, which is a careful representation of the 
principal muscular bands, most of the bands begin or are attached to the body-wall on 
a line running through sete 1 and 2 and ending in a line running through sete 
3 and 4. But there are some which begin more ventrally and end more dorsally 
than either couple of setze. In somite xviii most of the fascicles run in right angle 
to the median line, but the most posterior one as well as one or two more run diag- 
onally backwards. In somite xvii there is one large group of fascicles beginning 
around the male pore and running transversely sideways, while another group of fas- 
cicles run diagonally forward connecting the male region with the anterior part of 
the somite. There are also longer fascicles anterior of the male pore which run much 
further sideways than the outer sete. In somite xvi there are but few fascicles, 
much smaller and shorter. The male pore and spermducts are so entirely covered 
up by these muscular fascicles that they can only be seen with the greatest difficulty 
when viewed on the spread body-wall. In the figure (fig. 7), only the principal mus- 
cles of one side are drawn. The shaded bands which are seen crossing the median 
line are slight ridges in the body-wall, connecting the principal muscle fascicles. The 
objects of these muscles are of course to elevate and depress the male zone. Similar 
muscles were first described by Benham in Moniligaster, and later by myself in Argi- 
lophilus. They no doubt exist in most species of Oligochzeta but are of great interest 
and yalue as species characteristics. 
The septa begin between somites vy and vi, and gradually increase in size 
toward somite ix. The most anterior septum, however, is not unusually thick. The 
following three septa are very thick, that between viii and ix being the thickest. 
Alimentary canal. The buccal cavity is very large and occupies somites i and 
ii. Pharynx begins in ili or posterior part of ii and extends to the posterior part of 
iii. It is only developed superiorly and merely attached to the cesophagus in the pos- 
terior part of ii. Qisophagus consists of one in the beginning narrow and compara- 
tively even duct, which in iy rises upwards and then becomes considerably sacculated 
