THE HABITS AND STRUCTURE OF ARENICOLA MARINA. 121 



FlG. 8. — Papilla? in situ on the base of the proboscis of young ■worm, x 6. 



FlG. 9. — A group of neuropodial setae from a very young Arenicola marina 

 16 mm. long. The shape and strongly-toothed ridge distinguish these seta? 

 from those of the adult (Figs. 11 and 12). The youngest seta? are on the left 

 side of the figure, x 300, 



FlG. 10. — Notopodial seta 6 mm. long, x 16. 



FlG. 10a. — The tip magnified, x 50. 



FlG. 10b. — The toothing on the notopodial seta highly magnified, x 450. 



FlG. 11. — Neuropodial seta ( x 20), and enlarged ( x 120). 



FlG. 12. — A group of developing neuropodial seta? in situ in the neurpodium 

 {Nm.) of a " Laminarian " specimen, x 70. Proc. is referred to on p. 9. 



FlG. 13.— The fourth and fifth cha?tigerous segments of the left side of a 

 large mature "Laminarian" specimen. The first two nephrida are shown. 

 The figure is a study of the blood-vessels of the nerve-cord, of the oblique 

 muscles, and of the connection between the nephrostomial and the dorsal 

 longitudinal vessels {D.L.V.). x 3f. 



FlG. 14. — The first nephridium from the specimen shown in Fig. 13, seen 

 from the dorsal surface, to show the gonidial vessel (67. F 1 .) bearing blind, 

 vascular processes. The gonidial vessel on this nephridium is sterile, x 4. 



FlG. 15. — Fifith right nephridium of an adult male, to show the bladder 

 distended with spermatozoa. The nephrostome is widely open. Seen on 

 February 24th, 1897. x 4. 



FlG. 16. — The second nephridium of the right side of a specimen 29"5 mm. 

 long seen from the dorsal surface, to show the gonidial vessel (67. F.), the 

 commencing processes of the dorsal lip, and the position of the external 

 opening (No.-) with regard to the neuropodium [Nm 5 .). The ventral lip of 

 the nephrostome (V.Nph-.) is seen through the dorsal one. x60. 



FlG. 17.— Funnel of the first left nephridium from the same specimen as 

 Fig. 16. seen from the right side, to show the vertical position of the nephro- 

 stome and the commencing processes on the anterior lip. x 90. 



Plate IX. 



FlG. 18. — The second right nephridium from a specimen 44 mm. long. 

 Dorsal view, to show the remarkably complete capillary circulation and the 

 extension of the vessel of the dorsal lip to form the gonidial vessel (67. V.). 

 The ventral lip (F".A7p/i 2 .) is seen by transparency, x 65. 



Fig. 19. — Three views of the anterior end of a specimen 8 inches long 

 (littoral variety), to show the prostomium, nuchal organ, openings of the 

 otocysts, and the secondary annulation of the skin. A. From the left side. 

 B. From above. C. From below. x 12. 



FlG. 20. — Transverse section across the middle of the prostomium to show 

 the brain, the three prostomial lobes, and the rich blood-supply of this region. 

 The brain lies in the central prostomial lobe, and its covering of ganglion- 

 cells is closely applied to the overlying sensory epithelium. The section is 

 cut across in the region of the posterior cerebral cornua (P.Cr.). x 65. 



Fig. 21. — Transverse section of the same series as Fig. 20, across the 

 nuchal organ, Nu, the hinder cornua of the brain, and one otocyst, with its 

 contained otoliths, x 65. 



