310 W. BLAXLAND BENHAM. 
Fic. 6.—A portion of Fig.3, more enlarged (x 8). It represents the pros- 
tate of the eighth side; the numbers are placed nearly in the mid-ventral 
line. Prst. Prostate. a. Its free extremity. pe. d. Penial duct. pe. s. Sac 
with penial chetz. 
Fic. 7.—The sac of the penial chete, which protrude from its cut end 
which is turned forwards, and the prostate are cut away to show the sperm- 
duct (sp. d.) entering the body-wall in Somite xv1II. 
Fic. 8.—A diagrammatic longitudinal section through this region of the 
body-wall, to show the pores of the penial duct of the sac with penial chete, 
and of the sperm-duct. [It is compiled from a series of sections.] cz. Circular 
muscles of the body-wall. ep. Epidermis. /y. Longitudinal muscles of the 
body-wall. je. ch. One penial cheta in the sac (pe. s.). pe. d. Penial duct 
opening to the exterior, independently of the sac of penial chet. pores. 
Aperture common to the prostate duct and penial sac. Prst. Prostate. 
pr. pap. Papilla carrying the pore of the prostate and penial sac. sp.d. Sperm- 
ducts. sp. p. Spermiducal pore. v. ch. Ventral cheete. 
Fic. 9.—The sac with penial chete; it was broken in removing it from 
the body, and the two portions @ and 4 are really continuous at «. 
Fic. 10.—A portion of one of the long penial chete, very highly magnified 
to show the notched ridges and the triangular section. It is surrounded by 
the cuticular membrane (m.) which lines the sac. 
Fie. 11.—Transverse section through the prostate. a is the celomic epi- 
thelium surrounding it. dv. Blood-vessels in the wall. Only a few cells are 
represented in detail, the rest in outline. 
Fic. 12.—Transverse section of the penial duct. ep. Its epithelium. m. 
Its muscular coat. v. Blood-vessels. 
Fie. 13.—The spermatheca of the right side. s. The chief sac. app. The 
appendix or diverticulum. d. The duct penetrating the body-wall. 
Plagiocheta punctata.—Fies. 14 to 32. 
Fic. 14.—Dorsal view of the worm (x 2), to show the characteristic 
marking (from a spirit specimen). c/. Clitellum. pr. Prostomium. 
Fie. 15.—Dorsal view of anterior end of worm, showing the shape of the 
prostomium. 
Fic. 16.—Ventral view of the anterior 23 somites, showing the charac- 
teristic arrangement of the chet (represented by dots) in couples, the 
position of the nephridiopores (xe. 0.), the pores of spermathece (sp//.) in 
depressions, the prostate pores (prst.', prst2) also in a depression. clit. 
Clitellum. m. Mouth. pro. Prostomium. 
Fic. 17.—A transverse section of the worm behind the clitellum, showing 
the way in which the longitudinal muscular coat (/y.) of the body-wall is 
