636 R. J. HARVEY GIBSON ON THE 



Fig. 14. Epithelium from the outer aspect of the ocular swelling ( x 500). a, cuticle; b, columnar 



cells ; c, pointed short cells ; d, subepithelial connective tissue ; e, trahecuke. 

 Fig. 15. Longitudinal section of eye ( x 250). a, ocular pit and retina. 



PLATE CL. 



Fig. 16. Retina ( x 800). a, cuticle with two layers, b, prisms separating them; c, pigmented epithe- 

 lium ; d, nerve plexus. (This figure was drawn from a preparation in which the cilia were 

 wanting.) 



Fig. 16a. Arrangement of pigment granules iu the columnar cells ( x 800). 



Fig. 17. Transverse section through neck behind the origin of the tentacles, ph., pharynx; s., salivary 

 gland; p., palate; r., radula; m.s., muscle of infraradular sheet ; I.e., lateral cartilage ; a.c, 

 anterior cartilage; l.p., lateral protractor; v.pr., ventral protractor; u.p., under plate; 

 v.tr. and v'.tr '., ventral transverse muscles ; l.m., longitudinal muscle. 



Fig. 18. Epithelium covering the attachment of the mantle to the shell in the head region ( x 250). a, 

 epithelium ; b, subepithelial layer ; c, muscle. 



Fig. 19. Vertical section of circular muscle ( x 50). a, epithelium; b, blood vessel; c, vertical 

 muscle; d, epithelium of side of foot; e, circular muscle (deep); h, circular muscle 

 (superficial) ; /, nerves ; g, dense connective tissue beneath the epithelium of foot. 



Fig. 20. Section of the mantle ( x 50), (see fig. 18). a, epithelium; b, lacunar blood spaces; c, 

 mantle muscle. 



Fig. 21. Muscular fibres of foot ( x 500). 



Fig. 22. Shell, with muscle, &c. impressions (interior), (n.s.). m.a., mantle attachment; cm., circular 

 muscle attachment; v., visceral attachment; d., dorsum, not touched by viscera. 



Fig. 23. Shell (exterior) (n.s.). 



Fig. 24. Radial section, mantle and gill processes ( x 50). a, papilla ; b, nerve ; c, efferent branchial 

 vein; d, gill lamella; e, muscle; /, afferent branchial veins. 



Fig. 25. Epithelium of the dorsum of the mantle ( x 500). a, epithelium; b, circular muscle fibres; c, 

 radial muscle fibres; d, connective tissue; e, muscle fibres connected with epithelial cells; 

 /, deep radial muscle. 



Fig. 26. Epithelium covering the under surface of the mantle ( x 250). a, surface ; b, side view. 



Fig. 27. Epithelium of the mantle at the origin of gill lamella? ( x 500). 



Fig. 28. Mantle, radial section, with swollen branchial vein ( x 30). a, cavity of papilla ; b, nerve 

 ganglion ; c, lacuna? ; d, efferent branchial vein ; e, transverse trabecula? ; f, radial 

 muscle ; g, afferent branchial vein. 



Fig. 29. Connective tissue cells of same ( x 500). 



Fig. 30. Part of gill lamella ( x 100). 



PLATE CLI. 



Fig. 31. Mantle papilla, longitudinal section ( x 100). a, ganglion and nerves; b, nerve fibres; 

 c, vascular lacuna? ; d, blood corpuscles. 



Fig. 32. Epithelium of the dorsal wall above the pit of papilla ( x 250). 



Fig. 33. Epithelium of papilla ( x 250). - 



Fig. 34. Nephridia, A, left; B, right ( x 50). c, fibrous septum; a.a', blood vessels in the walls of the 

 nephridia ; b, left renal epithelium ; e, right renal epithelium ; d, cavity of right neph- 

 ridium ; /, cavity of left nephridium ; g, epithelium of nephridia on surface view. 



Fig. 35. Renal epithelium, right nephridium ( x 250). 



Fig. 36. Pericardium interior, looking towards the right shoulder ( x 20). a, right renal papilla ; b, 

 anus ; c, left renal papilla ; d, pericardium ; e, pericardial opening of the left kidney ; /, 

 pericardial opening of right kidney; g, right aorta; h, rectum. (This figure is senii- 

 diagramatic, and compounded from several preparations.) 



Fig. 37. Renal epithelium, left nephridium. 



Fig. 38. Branchial vein and vcinlets ( x 50). a, gill lamella?; b, circular muscle; c, common 

 branchial vein; d, afferent branchial vcinlets from the mantle skirt; e, efferent branchial 

 vcinlets. from the gills to branchial vein proper; /, branchial vein of right side. 



