246 E. A. ANDREWS. 



PLATE XIV. 



Figure 11. Transverse section of anterior end of body near 

 extreme tip of notochord, at line (a) Fig. 4. 



Figure 12. Transverse section at anterior end of pre-oral 

 chamber, line (6) Fig. 4 : the pre-oral pit, ciliated ridge and 

 blood vessel are shown on the animal's right, the tips of some 

 cirri within the chamber. 



Figure 13. Transverse section at the posterior part of the pre- 

 oral chamber, line (c) Fig. 4, showing the right ciliated ridge and 

 blood vessel of the Rtiderorgan. 



Figure 14. Transverse section of the middle of the body, at 

 (d) Fig. 4, showing the position of the ovary on the animal's right 

 side. The pharyngeal basket and the lining of the atrium are 

 indicated diagrammatically. 



Figure 15. Transverse section at (e) Fig. 4, where the atrium 

 is ending in a spout, the free tip of which is shown. Two post- 

 atrioporal pouches are seen within the coelorae. 



Figure 16. Grouping of muscle fibers in the right and the left 

 sub-atrial ridges of a young larva ; from longitudinal, horizontal 

 sections. The limits of a myotome are marked by crosses. 



Figure 17. Optical longitudinal section of three dorsal fin-rays 

 and fin-ray spaces, from a preserved specimen stained alive by 

 Bismarck brown. Certain large cells at the top of each chamber 

 and parts of two dorsal lymph canals are shown. 



Figure 18. Right ciliated ridge, pre-oral pit and anterior end 

 of pre-oral chamber seen in horizontal, longitudinal section. 



Figure 19. Optical, longitudinal section of the free part of a 

 pre-oral cirrus with its axial skeletal rod. From a preserved 

 specimen. 



Figure 20. Transverse section of the anterior union of the ventral, 

 metapleura-like ridges bounding the edges of the pre-oral chamber. 



Figure 21. Transverse just anterior to anus, at line (/) Fig. 4, 

 showing the median fin extending down from the right towards a 

 median position. 



Figure 22. Transverse section at the anus, (g) Fig. 4, with the 

 median fin still on the right of the animal. 



