EXPLANATION OF THE I'LATES. 
5; 
PLATE II. 
ILLUSTRATING THE REDUCED PROTRACTOR PEDIS MUSCLE, &c. 
Fig. I. — American oyster, with lialf of the left valve {c.s.) removed, to show the insertion of the reduced 
pedal muscle at ,7). 
Fig. 2. — American oyster, with well-marked " spot " (.s/<.) formed by pedal muscle. 
Fig. 3. — Another specimen, with the edge of the spot strongly pigmented ( x 2). 
Fig. 4. — Section across the adductor impression of the shell ( x 2). The thin black line is dark brown 
pigment. 
Fig. 5. — One end of a similar section magnitied : ((, prismatic layer ; b, opaque chalky layer ; e, trans- 
parent columnar lining to adductor impression ; d, brown pigment (Swift, obj. i inch\ 
Fig. 6. — Three sections across the impression formed on shell by insertion of pedal muscle. The smaller 
black marks are brown pigment ( x 2). 
Fig. 7. — One end of a similar section magnified. Lettering as in Fig. 5 (Swift, obj. i inch). 
Fig. 8. — Epithelium on surface of mantle near " spot," for comparison with, 
Fig. 9. — Modification of surface of mantle at "spot" (Leitz, obj. 7). 
Fig. 10. — Section showing the fibres of the pedal muscle leaving the spot and running inwards and back- 
wards (Leitz, obj. 3). 
Fig. II. — Section further back, showing the muscle fibres coming into close relation with the large blood 
sinus (lac.) and with the renal tubules. 
Fig. 12. — Section still further back, showing the fibres cut nearly transversely, and now lying below the 
blood sinus and near the liver tubules. 
Fig. 13. — Last section of the series, showing the distribution of the muscle fibres along the top of the 
anterior end of the external gill (all Leitz, obj. 3). 
Fig. 14.— Diagram to show the action of the modified protractor pedis muscle (pr.) in widening the two 
ciliated food avenues (see arrows) leading to the mouth («t.). 
PLATE HI. 
ILLUSTRATING THE LIVER, &c. 
Fig. I. — Oblique section of the visceral mass and gills of an oyster, to show relations of stomach [sL), 
liver (L), pallial lobes {pali.\ and the 4 branchi;e {(jr.), natural size. 
Fig. 2. — Section of a visceral mass, to show a dark coloured liver, natural size. 
Fig. 3. — Similar section showing a light yellow brown liver, natural size. 
Fig. 4. — Low-power view of a section of visceral mass of a green Dutch oyster, to show stomach (t>t.}, 
intestine (i.i.), liver ducts (d.d.d.), and c;eca of liver {v.r.c.) ; (Swift, obj. i inch). 
Fig. 5. — Section showing the opening of a liver duct into the stomach (Leitz, obj. 3). 
Fig. 6.— Longitudinal section of a liver c;ccum (Leitz, obj. 7). 
Fig. 7. — Transverse section of a liver ca:cum (Leitz, obj. 7). 
Fig. 8. — Transverse section of a well-formed liver ctecmn of a green Dutch oyster (Leitz, obj. 7;. 
Fig. 9. — Three liver cells from the last, showing green granules in the cells (Zeiss, apochr. r5 mm.). 
Fig. 10. — Section of a group of healthy, well-formed liver cteca (Zeiss, iV obj.). 
Fig. II. — Section of a group of shrunken, degenerate liver caeca, from a sickly Fleetwood American 
oyster (Zeiss, tV obj.). 
Fig. 12. — Hepatic cells {/i.e.), basal cells or " Fermentzellen '■ (Jj.':.), connective tissue {u.f.), green 
leucocyte (L), from liver cfecum of green oyster with green granules {(/ii. ;//■.) in the liver cells 
(Zeiss, apochr. 1 5 mm ). 
E 
