PACIFIC COAST OLIGOCHyETA. 75 



between setie 1 and 1 with the usual hiyers less the glandular cells (fig. 41, b. d.) 

 marking the points where the clitellura 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 tliickening of this layer is readily understood wheti we view one of the 

 sections of this region. The part of the body-wall, on which I'ests 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 arc soon to spread out 

 from the male pore laterally, connecting the center of somite xviii witli 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 prominoutand 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, c. c; fig. 41, c. 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 b}' what looks like connective 

 tissue. The size of this copulatory cushion is very great; not only do these swellings 

 project considerably outward l)ut 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 papilte. 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 vertical, longitudinal section, more 

 interior to the lai-ge 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, c. t.), 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 s;). vi.) The large strand s/>. m in fig. 42, connects the bend of the prostate, where 

 enters the sperm duct, with the ventral part of the body-wall under the ventral nerve- 

 cord . 



