PACIFIC COAST OLIGOCHATA. iD 
between sete 1 and 1 with the usual layers less the glandular cells (fig. 41, 5. ¢/.) 
marking the points where the clitellum ceases. We have thus before us a species 
with a dorsal and lateral clitellum in some somites, and with a ventral and lateral in 
one somite. 
In all of the clitellar somites the inner or longitudinal muscular layer possesses 
an enormous development laterally, especially so in the region of the prostate, where 
it reaches a width four times that at the dorsal and ventral part. The reason of this 
enormous thickening of this layer is readily understood when we view one of the 
sections of this region. The part of the body-wall, on which rests the prostate, is 
attached by numerous arciform muscular bundles, arranged in a fan-shaped manner, 
to the dorsal and lateral sides of the body. These muscles are more numerous and 
stronger than any I have seen described in other species, making it possible for this 
region of the body to contract in a most characteristic manner. 
When the body is opened and flattened out these muscles are seen to spread out 
from the male pore laterally, connecting the center of somite xviii with the two 
nearest somites xvii and xix as I have endeavored to show in fig. 42. As may be 
judged from the figure the muscles are arranged in regular fascicles of which we may 
count twenty-two to twenty-four as being more prominent and overlapping the other— 
a smaller number of fascicles situated below. The wider periphery of the attachment 
is situated on the body-wall above the prostate, but the lower and narrower part of 
the attachment of the fan is situated on a peculiar swelling which I have designated 
as the copulatory cushion (fig. 42, ¢. ¢.; fig. 41, c. ¢.; fig. 38, ¢c. c.; figs. 44, 45), 
apparently a thickening of the longitudinal muscular layer, transversed by innumer- 
able other muscles in every direction, all connected by what looks like connective 
tissue. The size of this copulatory cushion is very great; not only do these swellings 
project considerably outward but inwardly they encroach to a great extent on the 
internal cavity, especially so in mature specimens. This peculiar organ is entirely 
muscular, there being no sign of any outwardly opening papillae. The prostate pore 
is situated between this cushion and the projection caused by the increased thickness 
of the longitudinal layer and the contraction of the fan-shaped muscles. In fig. 43 
the section, a longitudinal one, is somewhat oblique, having followed the large muscular 
strands which surround the outlet duct of the prostate as well as the muscles of the 
copulatory cushion. Fig. 44 represents a more yertical, longitudinal section, more 
interior to the large fan-muscles, which do not show in the section except their inner 
attachments (a. m.) The large arciform strands vary considerably in size, those 
nearest the body-wall being the smallest, those nearest the intestine the largest. 
When a cross-section through somite xviii is viewed it will be seen that the smaller 
strands are filled between with connective tissue (fig. 41, ¢. ¢.), while a concentric 
transverse muscular strand is crossing them near the inner angle of the prostate pore. 
Other muscles connect the glandular prostate with the body-wall (figs. 37, 40 m and 
42 sp.m.) The large strand sp. m in fig. 42, connects the bend of the prostate, where 
enters the sperm duet, with the ventral part of the body-wall under the ventral nerye- 
cord, 
