294 GILBERT C. LOURNE. 



aperture. /«. Moutli. ??i/. Muscle fibres, m^. Left mantle lobe. ?«^'. Right 

 mantle lobe. oc. CEsopliagus. f.c.c. Pericardial cells willi endoplastic con- 

 cretions, pd-j. Pedal ganglia, 'pl.m- Brancbio-pallial muscle, pr-f. Poste- 

 rior retractor pedis muscle, r. Rectum, r.cp. Right cerebro-pleural ganglion. 

 r.ep. Right excretory pore. r.li. Right kidney, r.p.g. Right pericardial 

 gland, r.rp. Right reuo-pericardial aperture, rt. Retina, st. Stomach. 



V. Ventricle of heart, v.cm.l. Left visceral connective. v.cm.r. Right 

 visceral connective, vel. Velar fold of gill filaments, v.tj. Visceral ganglia. 

 vi. Vitreous body. v.m. Visceral mass. x. The dorsal pallial suture, z. 

 Cavities between various ))arts of the body, ending blindly and serving for 

 storage of water, i. Reflected lamella of lelt external demibranch. li. Direct 

 lamella of left external demibranch. iii. Direct lamella of left internal 

 demibranch. iv. Reflected lamella of left internal demibranch. v. Union 

 between the reflected lamella of the right and left internal demibranclis. 



VI. Reflected lamella of right internal demibranch. vii. Direct lamella of 

 right internal demibranch. viii. Direct lamella of right external demibranch. 

 IX. Reflected lamella of right external demibranch. 



PLATE 15. 



Fig. 1.— View of the animal lying in the left valve of the shell, after 

 removal of the right mantle lobe, x about 2|. 



Fig. 2. — The animal removed from its shell and viewed from the left side, 

 showing the ring of pallial eye-spots. The principal organs of the left side 

 are seen through the transparent left mantle lobe. 



F[G. 3. — A reconstruction from a series of sections to show the course of 

 the alimentary canal and the nervous system. 



Fig. 4'. — A reconstruction from a series of sections to show the renal 

 organs and the extent and relations of the pericardial glands. The right 

 kidney is represented in a darker, the left kidney in a lighter tone. The 

 spaces enclosed by the black lines represent the pericardial glands. 



Fig. 5. — A horizontal section through the angle of the direct and reflected 

 lamellae of one of the demibranchs, showing the single row of ciliated discs, 

 c.d. Highly magnilied. 



Fig. 0. — A transverse section through three velar filaments, showing the 

 stiff cilia, c.v., on the ventral faces of the filaments. Zeiss' -^^ Lom.imm. 

 comp. oc. 4. 



Fig. 7. — A transverse section through two adjacent gill filaments. Zeiss' 

 ■^ hom. imm., comi). oc. 4. 



■ Fig. 8. — A transverse section through a pallial fold guarding the entrance 

 to one of the water reservoirs, showing the ciliated ridge, c.r., on the edge of 

 the fold. u. A branch of the pallial nerve. 



