430 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
EXPLANATION OF PLATES. 
[Drawings by the author.] 
Plate LXXIX. 
Ostrea virginiana — Oyster: 
Fig. 1. Vertical transverse section of anterior edge of mantle (m), outer and inner palps (op and 
ip), and bv, blood vessel. 
Fig. 2. Same, through posterior end of stomach, s; g, generative mass; l, liver; i, intestine; w, 
water- tube of gill ; ol, outer lamella of gill ; il, inner lamella ; og, outer gill ; ig, inner gill ; 
brc, branchial chamber; vie, mantle edge. 
Fig. 3. Same, posterior to stomach; epc, epibranchial chamber ; ilc, interlamellar connection. 
Fig. 4. Same, through region of heart; r, rectum; h, heart; p, pericardium. 
Plate LXXX. 
Ostrea virginiana — Oyster : 
Fig. 5. Slightly posterior to last. The epibranchial chamber of the right side of the animal ( and of 
the section, epc) extends dorsally and opens to the exterior above, between the mantle 
. edges. The mantle is here figured as being applied to the body above, but in reality it is 
entirely free from it. 
Fig. 6. Same, through anterior of adductor muscle, a. 
Fig. 7. Same, through middle of adductor muscle, a. This figure shows the generative mass, g, 
extended nearly to the end of the rectum, r, dorsally, and also far beneath the adductor. 
Fig. 8. Same, through posterior of adductor ; g, generative mass at extreme posterior end of vis- 
ceral mass ; cl, cloacal chamber. 
Fig. 9. Same, through cloacal chamber posteriorly; x, ridge running backward on inner wall of 
mantle, continuous with line of concrescence of gill to mantle. 
Venus mercenaria — Quahog : 
Fig. 10. Vertical, transverse section through mouth, mo, and oesophagus; s, anterior end of 
stomach, into which opens oesophagus; l, liver; g, generative mass; pi, palp (the anterior). 
Plate LXXXI. 
Venus mercenaria — Quahog : 
Fig. 11. Vertical, transverse section through stomach, s ; me, mantle edge; l, liver; g, generative 
mass; ar, anterior foot-retractor ; ec, epibranchial chamber ; ig, inner gill ; m, mantle. 
Fig. 12. Same, through junction of anterior foot-retractors, ar, with the foot,/; Id, liver duct. 
Fig. 13. Same, through posterior end of liver ; mus, scattered transverse muscle fibers, just beneath 
visceral mass. Three marked lines of vertical muscles are also shown. 
Fig. 14. Same, through region of posterior end of stomach, s ; il, inner lamella of inner gill; mf, 
transverse muscle fibers in the generative mass, g. 
Plate LXXXII. 
Venus mercenaria — Quahog : 
Fig. 15. Vertical, transverse section in region of anterior end of heart, which contains rectum, r ; 
p. pericardium ; aw, auricle ; g, generative mass ; i, intestine ; me, mantle edge ; ec, epibran- 
chial chamber; il, inner lamella of inner gill; og, outer gill; mf, muscle fibers in visceral 
mass; /, foot. 
Fig. 16. Same, through region of ventricle of heart, h; p, extremely large pericardium; ngl, non- 
glandular part of nephridium ; gl, glandular part of nephridium; ol, outer lamella of outer 
gill, showing foldings. 
Fig. 17. Same, through region of posterior end of heart, h; mo, wall between nephridia; pr, poste- 
rior foot-retractors joining foot, f ; n, nephridium. 
