ON THE DIPLOCHORDA. 365 



List ojf References. 



1. S. F. IIarmek.— '" Challenger" Reports,' vol. xx, Appendix to (3). 



2. W. C. McIntosu. — '"Challenger" Reports,' vol. xx, on Ceplialo- 



discus dodecalophus. 



3. E. A. Andrews. — ' Journ. Morpb.,' vol. v, 1891. 



4. A. Lang.— ' Jcnaisclie Zeitschrift,' xxv (1890), pp. 1—12. 



KEY TO PLATES 23—26, 



Illustrating Mr. A. T. Masterman's paper " On the Diplo- 

 chorda : Part II. The Structure of Cephalodiscus." 



PLATE 23. 



Fig. 1. — Transverse section of the epistome of Cephalodiscus dode- 

 calophus, showing only the central area. 

 Fig. 2. — Ditto, from same series, next section. 

 Fig. 3. — Ditto, ditto, third section. 

 Fig. 4. — Ditto, ditto, fourth section. 

 Fig. 5. — Ditto, ditto, sixth section. 

 Fig. 6. — Ditto, ditto, ninth section. 

 Fig. 7. — Ditto, ditto, twelfth section. 

 Fig. 8. — Ditto, ditto, seventeenth section. 

 Fig. 9. — Ditto, ditto, eighteenth section. 



PLATE 24. 



Fig. 10. — Ditto, ditto, nineteenth section. 

 Fig. 11. — Ditto, ditto, twentieth section. 

 Fig. 12. — Ditto, ditto, twenty-third section. 



Fig. 13. — Sagittal longitudinal section (nearly) to one side of median line 

 to cut notochord, &c. 

 Fig. 14. — Ditto, of same series as Fig. 13, left side nearly median. 



PLATE 25. 



Figs. 15, 16, 17. — Nearly transverse sections, in order from before back- 

 wards. 



Fig. 18. — Transverse section of pharyngeal cleft, from a sagittal section of 

 same series as Figs. 13 and 14. 



