OLIGOTREMA PSAMMITES. 271 



PLATE 20. 



Fig. 7. — A section througli the mouth. 



FiCr. 8. — A section through the upper part of the branchial sac. 



Tig. 9. — A section through tlie middle of the branchial sac. 



Fig. 10. — A section through the lower end of the branchial sac. 



Fig. 11. — A section through the upper end of the oesophagus, showing the 

 thickening of the ventral suspensory fold, in which there are four small cavities, 

 two of them opening by stigmata into the right peribranchial cavity. 



Fig. 12. — A section through the middle of the oesophagus. 



Fig. 13. — A section through the lower end of the oesophagus. 



Fig. 14. — A section through the upper end of the stomach, showing the 

 origin of tiie intestine from the ventral limb of the stomach and the openings 

 of the oviducts. 



Fig. 15. — A section passing ihrough the atrial siphon and anus. 



PLATE 21. 



Fig. 16. — The inner surface of a portion of the wall of the branchial sac, 

 showing the longitudinal branchial folds, llie openings of two incurrent bran- 

 chial chambers, and the stigmata opening into the latter. This drawing is 

 made from a model reconstructed from a series of sections. 



Fig. 17. — Cells from the glandular epithelium of the oesophagus. 



Fig. is— 



a. Flagellate epithelium from the oral tentacles. 



I/. — Flagellate cells resembling collar-cells from the epithelium of the 

 branchial sac. 



c. — A portion of the e])ithelium of the branchial sac, showing the transi- 

 tion from the elongated flagellate cells to the ciliated epithelium of the 

 endostyle. 

 Fig. 19. — Transitional epithelium from the oesophageal groove. 

 Fig. 20. — Ciliated cells from the lips of the oesophageal groove. 

 Fig. 21. — An enlarged drawing of the openings of the oviducts into the 

 atrium. 



Fig. 22. — Part of a section through the upper region of the stomach, 

 highly magnified, showing the opening of the right sperm-duct. 



Fig. 23. — A portion of the epithelium lining the cavity of the renal sac, 

 highly magnified. 



Fig. 21. — Two concentrically striated spherules from the renal sac, embedded 

 in tiie renal epithelium (Zeiss -^^ liom. inim. coinp., oc. S). 



