838 A. T, MASTERMAN. 



pb. Proboscis vesicle, p. a. Perianal band. p. a. n. Pre-oral nerve-ring. 

 p. s. Perianal sinus, p. p. Proboscis pore. r. s. Ring sinus, sh. Sheath of 

 notochord. s. n. Subneural gland, s. ti. s. Subneural blood-sinus, s.p. 

 Sense papilla. s(. Stomach. L Tentacle, v. c. Ventral collar area. v. c. r. 

 Ventral ciliated ridge, v. ch. Ventral chordoid area. v. Vacuoles, v. c. n. 

 Ventral collar nerves, v. m. Ventral mesentery. 



PLATE 18. 

 Fig. 1. — Lateral view of entire larva with ten pairs of arms. 

 Fig. 2. — Lateral view of later larva, showing the distribution of the main 

 nervous tracts. 



Fig. 3. — Dorsal view of larva a little later than Fig. 1. 



Figs. 4 and 5. — Two positions commonly assumed by living larva. 



PLATE 19. 



Fig. 6. — Transverse section of fully developed larva in region of pre-oral 

 hood. 



Fig. 7. — Transverse section of same larva behind the nerve ganglion. 



Fig. 8. — Ditto, through mouth. 



Fig. 9. — Ditto, through notochords and oesophagus. 



Fig. 10. — Ditto, through collar region. 



Figs. 11 — 15. — Transverse sections of dorsal wall of same larva, between 

 Fig. 6 and Fig. 7, to show nerve ganglion. 



Fig. 16. — Transverse section of same larva through collar and trunk. 

 Fig. 17.— Ditto ditto, further back. 



PLATE 20. 



Figs. 18—20. — Sagittal sections of fully developed larva. Fig. 20 is nearly 

 median. 

 Figs. 21 — 27- — Coronal sections of ditto, with hood turned back. 

 Fig. 28.. — Transverse section of hood. 

 Fig. 29. — Obliquely transverse section to show oral grooves. 



PLATE 21. 



Fig. 30. — Surface of notochord in early larva. 



Figs. 30a, 30b, 30c. — Transverse sections of notochord in Fig. 30 at A, 

 B, and c respectively. 



Fig. 31. — Transverse section of later stage of notochord. 

 Fig. 32. — Longitudinal section of later stage of notochord. 



