430 BULLETIN OF THE UNITED teTATES FISH COMMISSION, 



EXPLANATION OF PLATES. 



[Drawings by the author.] 



Plate LXXIX. 



Ostien lirginiana — Oyster: 



Fui. 1. Vertical traiisveise section of anterior edge ol mantle (w), outer and inner palps (i>2> and 



ijj), and br, blood vessel. 

 Fig. 2. Same, through posterior end of stomach, s; g, generative mass; /, liver; i, intestine; ir. 



water-tub<- of gill; ol, outer lamella of gill; il, inner lamella; og, outer gill; ig. inner gill ; 



hrc, branchial chamber; mc, mantle edge. 

 Fi<f. 3. Same, ijosterior to stomach: cj^c, epibranchial chamber : i/c, iuterlamellar connection. 

 Fig. 4. Same, through region of heart; /•, rectum: /*. heart; p. pericardium. 



Plate LXXX. 



0>t(na virginiana — Ojisier : 



Fig. "). Slio-htly posterior to last. The epibranchial chamber of the right side of the animal (and of 

 the section e/jc) extends dorsally and opens to the exterior above, between the mantle 

 edo-es. The mantle is here tigured as being applied to the body above, but in reality it is 

 entirely free from it. 



Fig. (5. Same, through anterior of adductor muscle, ti. 



Fig. 7. Same, through middle of adductor muscle, «. This figure shows the generative mass. //. 

 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 ma.ss ; cl. cloacal chamber. 



Fig. y. Same, through cloacal chamber posteriorly; .r, ridge running backward on iiimi wall of 

 mantle, continuous with line of concrescence of gill to mantle. 

 Veiutfi merceiiaria — Qiiahog : 



Fig. 10. Vertical, transverse section through mouth, mo, and cesophagus; s, anterior end of 

 stomach, into which opens (esophagus: I. liver; g, generative mass; pi, palp (the anterior). 



Plate LXXXI. 



I ■«•» It .•< m erceitari a — V " « '' "'/ •' 



Fig. 11. Vertical, transverse section through stomach, s ; «te, mantle edge; 1, liver; y, gencrati\c 



mass; «r, anterior foot-retractor ; ec, epibranchial chamber; k/, inner gill ; «i, mantle. 

 Fig. 12. Same, through junction of anterior foot-retractors, ar, with the foot,/; M, liver duct. 

 Fig. 13. Same, through posterior end of liver ; inns, 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 ; //, inner lamella of inner gill; mf, 



transverse muscle fibers in the generative mass. g. 



Plate LXXXII. 



Vennx merveiiaiia — Qiiahug : 



Fig. 15. Vertical, transverse section in region of anterior end of heart, which contains rectum, r; 

 !>, pericardium: an. auricle; g. generative mass : (. intestine: mc, mantle edge; ec, epibran- 

 chial chamber : (7, inner lamella of inner gill; of/, outer gill; «i/, muscle fibers in Wsceral 

 mass; /, foot. 



Fui. 16. Same, through region of ventricle of heart, /(,• p. extremely large pericardium; ngl, uon- 

 o-landular 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. //.• mr, wall between nephridia: jn: ))o.ste- 

 rior foot-retractors joining foot,/; n, nephridium. 



