ON THE DIPLOCHORDA. 417 



EXPLANATION OF PLATES 18—21, 



Illustrating Mr. Arthur T. Masterman's paper " On the 

 Diplochorda/' 



Abbreviations. 



arch. Arclieiiteroii. bp. Blastopore, be. Blastocoele. ent. Enteroii. m. 

 Mouth, vise. Mesocoele (collar cavity), mtc. Metacoele (trunk cavity), ng. 

 Nerve gaui,dion. p. Pre-oral hood. pc. Protocoele. sns. Subneural sinus. 

 st. Stoniodseum. t^, fi, fi. Pairs of tentacles. 



PLATE 18. 

 Fig. 1. — Embryo in egg-membrane. 

 EiG. 2. — Embryo with two blastomeres ; side view. 

 Fig. 3. — Embryo with four blastomeres; side view. 

 Fig. 4. — Embryo with four blastomeres; ventral view. 

 Fig. 5. — Embryo with eight blastomeres ; side view. 

 Figs. 6 — 10. — Lateral views of series of larvae. 

 Figs. 11 — 15. — Ventral views of series of larvae. 

 Figs. 16 — 18. — Lateral views of late larvae. 

 Fig. 19.— Ventral view of Fig. 18. 

 Fig. 20. — Mucus band with embryos. 



PLATE 19. 

 Pig. 21. — Transverse section of Fig. 3. 



Figs. 22 — 24. — Longitudinal sections of embryo later than Fig. 5. 

 Fig. 25. — Longitudinal sagittal section of Fig. 11. 

 Fig. 26. — Longitudinal sagittal section of Fig. 12. 

 Fig. 27. — Longitudinal sagittal section of Fig. 13. 

 Fig. 28. — Longitudinal coronal section of Fig. 13. 

 Fig. 29. — Longitudinal sagittal section of Fig. 9. 

 Fig. 30. — Longitudinal sagittal section of Fig. 10. 

 Figs. 31, 32. — Longitudinal coronal sections of Fig. 10. 

 F'iG. 33. — Transverse section of F'ig. 10. 



Figs. 34 — 39. — Series of transverse sections of Fig. 16 (early). 

 F'iGs. 40 — 44. — Transverse sections through late stage of Fig. 16. 



PLATE 20. 

 Fig. 45. — Transverse section through larva of Fig. 16. 

 F'iGs. 46, 47.— Longitudinal sagittal sections through Fig. 18. 

 F^lGs. 48, 49. — Transverse sections through Fig. 18. 

 Fig. 50. — Semi-diagrammatic half-larva at stage of Fig. 18. 



