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CALIFORNIA ACADEMY OF SCIENCES. 
PLATE XXXYV. 
PONTODRILUS MICHAELSENI. 
Cross-section through somite xvii of a mature specimen showing the development of the clitellar cells on the 
dorsal and lateral sides of the clitellum. vv. cl. ventral termini of the clitellar cells. d. v. dorsal vessel. 
s. i. sacculated intestine. neph. nephridium. gl. pr. glandular part of prostate. pr. m. muscular part of 
prostate. m. muscles connecting the prostate with the body-wall. ¢. m. transverse muscles. 1. m. longi- 
tudinal muscles. cl. clitellar cells. v. cl. ventral termini of the clitellar region. 
Cross-section through a strongly contracted, fully matured specimen, through somite xviii, showing the copula- 
tory cushions as fully developed, as wellas the clitellar cells on the ventral side. Unfortunately the only fully 
developed specimen at my disposal had been badly contracted, hence the cells appear smaller than they would 
have done in properly prepared specimens. c.c. copulatory cushions. a. m. arciform or fan-shaped muscu- 
lar strands, which contract the copulatory region. i. ¢. m. interior transverse muscular strand, ending 
respectively in the copulatory cushions and in the projecting ventral lobes of the body. Other letters as in 
the last four figures. 
The body-wall viewed from the inner side of somites xvii, xviii and xix, showing the genital region of the left 
side. pr. m. prostate muscles connecting this organ with the body-wall. a. m. arciform muscles connecting 
the copulatory cushion with the upper body-wall. c.c. copulatory cushion. sp. m. muscles connecting the 
body-wall with the prostate at the junction with the spermduct. sp.d. spermduct. 1 and 2s. first and 
second seta. v.c. ventral nervecord. gl. pr. glandular prostate. m. pr. muscular prostate. s. m. smaller 
muscles, fan-like arranged, confined entirely to the copulatory cushion. sp. d. p. spermiducal pore overlaid 
by muscles. s. septa. 
A somewhat diagonal longitudinal section through the body-wall and copulatory cushion in somite xviii. The 
section is parallel with the muscular fan of arciform muscles, passing through the copulatory cushion near 
but not through the body-wall. Illustrating the arrangement of the muscular strands around the prostate in 
the vicinity of the male pore. The letters indicate the same as in the preceding figure. 
A longitudinal section through the copulatory cushion and the body-wall, the section being almost vertical. 
pr. prostate, just leaving the arciform muscles, and immediately before bending down towards the prostate 
pore. m. muscles connecting the prostate with the body-wall. «. m. the entrance of the arciform muscles 
into the copulatory cushion. 
A horizontal section of the body through somite xviii and the copulatory cushions, showing their size and 
position, etc. 
