40 p. W. GAMBLE AND J. H. ASHWORTH. 



PLATE 3. 



Fig. G. — View of a vertical longitudinal section of Arenicola marina 

 taken somewhat to the left of the middle line. The thickness of ihe body- 

 wall is exaggerated. The stomach has been cut away behind the heart, 

 to show the oblique muscles and the second nephridium. The main blood- 

 vessels only are indicated, the object of tlie figure being to show the exact 

 position of the three diaphragms {Dphm. ^~^), of the buccal or proboscidal 

 sheath {B. Sh.), and the relations of these to the external segmentation. X 3. 



Fig. 7. — Chitinoid spines covering the buccal papillae of that part of the 

 proboscis which is first protruded during eversion. They may be compared 

 with the figures of "hooks" from the proboscis of Sipunculids (e.g. Phasco- 

 lion) shown in Seleuka, 'Die Sipunculiden.' Caustic potash preparation. 

 X 50. 



Fig. 8. — Papillse in situ on the base of the proboscis of young worm. 

 X 6. 



Fig. 9. — A group of neuropodial setfe from a very young Arenicola 

 marina 16 mm. long. The shape and strongly-toothed ridge distinguish 

 these setae from those of the adult (figs. 11 and 12). The youngest setae are 

 on the left side of the figure. X 300. 



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



Fig. 10a.— The tip magnified. X 50. 



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



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



Fig. 12. — A group of developing neuropodial setae in situ in the neuro- 

 podium {Nm.) of a " Lamiuarian " specimen. X 70. Proc. is referred to on 

 p. 9. 



Fig. 13. — The fourth and fifth chaetigerous segments of the left side of 

 a large mature " Laminarian " specimen. The first two nephridia 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 3|. 



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

 seen from the dorsal surface, to show the gonidial vessel ((?. F'.) bearing 

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

 X 4. 



Fig. 15.— Fifth 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. 



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



