DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 9539 
v. b. Ventral blood-vessel. Mesentery, by which it is attached to cesopha- 
gus. v. Valves in hearts. 
Fie. 6.—Section through a portion of anal nephridia. 4, B. Two tubes, 
one cut transversely, the other longitudinally, in which the peritoneum (p.) is 
slowly adherent to the nephridial cells (z.). C, D. Two other tubes, in which 
the peritoneum (p.) is separated by a space containing a coagulable fluid from 
the nephridium itself (z.). In every case the nephridial tubules have not yet 
acquired a lumen. 
Fig. 7.—Transverse section through two nephridial tubules to illustrate 
the specialisation of the protoplasm of the cells into a central and peripheral 
portion. 
Fic. 8.—Transverse section through longitudinal muscle-layer of newly- 
hatched worm. 0. Muscular fibres imbedded in a faintly granular matrix. 
These are closer together, and have a columnar arrangement in that part of 
the longitudinal muscular layer which lies nearest to the circular muscles. 
a, Cavities in the gelatinous connective-tissue matrix. 
Fic. 9.—Section through part of buccal cavity of advanced embryo. Hp. 
Epithelium of buccal cavity. 4. Circum-csophageal nerve-ring.  zeph. 
Duct of ‘ mucous gland.” 
Fic. 10.—Transverse section through posterior region of the body of an. 
advanced embryo. Nephr. Anal nephridia. Neph'. Their ducts leading to 
exterior of body; the apertures into the alimentary canal are not shown. 
Fie. 11.—Longitudinal section through a portion of the 9th segment. 
Ep. Epidermis. WM. Circular muscle-layer. 2M’. Longitudinal muscular 
layer. s. Septum. / Rudimentary funnel of nephridium, which lies behind 
the septum. At z a duct leads towards the exterior. 
Fie. 12.—Gonad (gon.) and nephridial funnel (fwan.) of one of the genital 
segments of an embryo of Stage C. 
Fig. 13.—Gonad (gon.) and funnel (funz.) of newly-hatched worm. 
Fic. 14.—Gonad (goz.) and commencing vas deferens (vas. def.) of the same 
individual. Sp¢. Septum. 
Fig. 15.—Gonad of an embryo of Stage D. y.c. Germinal cells. p.c. 
Peritoneal cells. . 
Fic. 16.—Longitudinal section through a portion of the anteriorly-placed 
segments of an embryo of Stage C, showing nephridial funnel. 
Fic. 17.—Two anterior segments of an embryo of Stage A, showing the 
nephridia. The segments are numbered. xeph. External orifice. Funnel. 
Fic. 18.—Anterior end of body of same embryo. S. Larval sense-organ. 
br, Brain. Stom. Stomodeum. Mes. Mesenteron. 
Fic. 19.—A portion of Fig. 16, enlarged to illustrate the structure of 
nephridial funnel, which has lost its cilia and is commencing to degenerate. 
