502 ALFRED GIBBS BOURNE. 



nephridia. te. 1 — 9, the nine pairs of testes, ep. Epididymes. /;e. Penis. 

 ov. The ovisacs, gl. Glandular enlargement of the oviducts. 



Fig. 6. — Pontobdella muricata, portion of external surface. ««. The 

 median dorsal line, b b. The median ventral line. I, II, III, and IV, the 

 annuli of one somite. I«. The most anterior annulus of the next somite. 

 neph. External apertures of the nephridia. (N.B. — These are wrongly placed 

 in I ff : they should have the same position as in I.) 



Fig. 7. — Pontobdella muricata, similar view. Clitellar region. — 5. The 

 only annulus of somite 5. 6. The anterior clitellar somite. g-p-$ . The 

 male genital pore. 7. The posterior clitellar somite, g. p.'^ . The female 

 genital pore. 8. Anterior annulus of somite 8. a, b. Rings devoid of papillae 

 at either end of the clitellum. 



Fig. 8. — Pontobdella muricata, diagram of an opened somite from the 

 central region of the body, showing the relation of the internal organs to the 

 annuli. On the right side is shown only the nephridial network, neph. fun. 

 Nephridial funnel, neph. ap. Position of the external aperture, n. and g. n. 

 Nerve-cords and ganglia, v. v. The ventral vessel, lying within v. s. the ventral 

 sinus, d. V. s. Dorso-ventral sinus, containing branch of nerve-cord and ne- 

 phridial funnel. I. v. Lateral vessel. l.s. Lateral sinus (diagrammatic). 

 br. Branchial dilatation. br.s. Sinus connecting it with lateral sinus, br.v. 

 Vessel opening into it. x. Muscular bands in the walls of lateral sinus. 

 m. rad. Dorso-ventral muscles, t. Position of the testis. The numbers I, 

 II, III, IV, and I a, mark the annuli as above. 



Figs. 9 — 14 represent portions of transverse sections, the relative size of 

 the various histological elements is accurately represented. For explanation 

 of the reference letters, see General References. 



Fig. 9.— Pontobdella. 



Fig. 10. — Clepsine. 



Fig. 11. — Piscicola. 



Fig. 12. — Branchellion. 



Fig. 13. — Hirudo. 7^ marks the point of transition of botryoidal 



Fig. 14. — Trocheta. i into vaso-flbrous tissue. 

 Fig. 15. — Hirudo, — Portion of a section stained with gold, showing sensory 

 epidermic cells, ep. sens., and nerves, n. 



Figs. 16 — 24. — From transverse sections through the anterior region of the 

 body. See General References. Figs. 16, 17, 19, 21, and 23 are drawn 

 to the same scale ; Figs. 18, 20, 22, and 24 are more highly magnified. 



Fig. 16. — Trocheta. te. Loops of testicular tubules, which are carried 

 forward into this region. 



Figs. 17 and 18.— ^Branchellion. 



Figs. 19 and 20.— Piscicola. 



Figs. 21 and 22.— Clepsine. 



Figs. 23 and 24.— Pontobdella. 



