ON THE STRUCTUEE OF iENIGMA iENIGMATICA. 295 



PLATE 16. 



Fig. 9. — A transverse section tlirougli the body at tlie level of tlie foot 

 f.ir. The "flCclic tiicuspide" of Poll. 



Fig. 10. — A transverse section passintr tlirougli tlie posterior li;ilf of the 

 byssus muscle. 



Fig. 11. — A transverse section passing tlirougli the ventricle of the heart. 



Fig. 12. — A transverse section passing through the middle of the adductor 

 muscle. 



Fig. 13. — A transverse section passing about 2 millim. in front of the anus. 



Fig. 14. — A section tlirougli the rigiit reno-pericardial canal and the 

 adjacent portion of the pericardial gland. Highly magnified. 



Fig 15. — A section through the ciliated funnel of the opening of the left 

 gonaduct of a male into the kidney. The columnar ciliated cells of the funnel 

 are conspicuous, go. A follicle of the testis, sp.d. Sperm duct. 



Fig. 16. — a. A group of pericardial cells containing small concretions. 

 b. A group of larger concretions from the pericardial gland of another 

 specimen of J<j n i g m a. 



PLATE 17. 



Fig. 17- — A transverse section through the byssus and byssogenous laminae. 

 X 600. 



Fig. is. — A transverse section through the distal end of a byssogenous 

 lamina and two adjacent laniella of the byssus. cU. Ciliated epithelial cells 

 at the sides of the lamina, grn. A mass of byssogen granules in the connective 

 tissue core of the laminae. Zeiss' J^ hom. imm., comp. oc. 4. 



Fig. 19. — Portion of a section through the wall of the ventricle of the 

 heart, showing ep. ext., the external epithelium; m.f.,i\\e branchial cardiac 

 muscle fibres; pc.c, the characteristic pericardial gland cells with endoplastic 

 concretions. 



Fig. 20. — A section through a pallial eye, showing the deep invagination of 

 the epithelium lining, the inner face of the mantle, and the modification of the 

 deeper invaginated cells to form a retinal layer. 



Fig. 21. — A portion of another section through a pallial eye. Zeiss' ^^ 

 hom. imm., comp. oc. 4. 



Fig. 22. — A portion of a section through the cacum of the crystalline style, 

 showing the ciliated groove, y^., and the tract of modified epithelium on the 

 dorsal side of it. The section is reversed in the drawing, so that the ventral 

 side is uppermost. 



Fig. 23. — A section through the right labial groove, close to the mouth. 



Fig. 24. — A section through the epithelium of the large intestine, spor. 

 Sporozoan parasites. 



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