240 PROCEEDINGS OF THE ACADEMY OF [1883. 



As to the disposition of the concretion, I can say that they are 

 found in the postrectal and sacular portions, thickl}'^ embedded in 

 the walls ; the tubular portion, which may be looked upon as 

 the duct to the glandular or sacular portion, also has them in the 

 first part of its course, as far as o (PI. X, fig. 10) ; they then become 

 scattered and rarer until we get to c, when they have entirely 

 disappeared. The whole interior portion of the organ is ciliated. 



EXPLANATION OF PLATE X, 



Fig. 1. Tracsveise section, about the middle of A. fluviatilis ; s, shell ; 

 m, mantle ; mc, musculus cochlearis ; F, foot ; qm, transverse 

 muscular fibres ; L, liver ; mg, stomach ; E, albuminous gland ; 

 D, intestinal canal ; K, gill ; exo, excretory organ or kidney. 



Fig. 2. Diagram of buccal mass and odontopbore ; m, moutb ; b, curved 

 arrow showing direction the food takes to (oe) oesophagus ; a, 

 anterior wall ; c, arrow showing direction of movement of 

 radula when licking (for x, see text) ; Od, odontopbore ; r, 

 radula. 



Fig. 3. Part of horizontal section of A. fluviatilis ; Inf, infundibukim ; I 

 and ct, tube connecting kidney (a) to pericardium ( P) ; Ht, 

 heart ; 6s, blood-space ; m, mantle ; R, rectum ; mc, musculus 

 cochlearis ; alb, albuminous gland ; Oo, parts of genital 

 organs. 



Fig. 4 a. Horizontal section of odontopbore of A. fluviatilis. 



Fig. 4 b. Transverse section of same. 



Fig. 5. Posterior part of a longitudinal section of odontopbore of Helix 

 aperta. 

 For explanation of the letters of the last three figures, see text. 

 All the figures, with the exception of fig. 2 and fig. 10 have been 

 drawn by means of a camera lucida 



Fig. 6. Transverse section of the ganglion olfactorium {Oo) ; Inf, infun- 

 dibulum ; m, mantle ; d, kidney ; Brc, branchial chamber. 



Fig. 7 and 8. Two transverse sections of the tentacular ganglion of left 

 side of A. fluviatilis ; n, nerve ; e, epidermis ; g, ganglion ; p, 

 enlarged epidermal cells ; /, groove ; c, cutis ; rm, retractor 

 muscle ; au, eye. 



Fig. 9. Longitudinal section of upper lip of A. lacustris. For a, see 

 text. 



Fig. 10. Diagram of kidney of A. fluviatilis. For letters, see text. 



