ANATOMY OF THE PEARL OYSTER. 73 



PLATE IV. 



Pig. 1. Outer surface of the mantle, as seen from left side on removal of valve, to show the number and 



arrangement of the insertions of the pallial muscles; nat. size. Add., adductor muscle; 



Ret., retractor muscle ; Lev.a. and Lev.p., anterior and posterior levators. 

 Pigs. 2 to 6. Drawings of the interior of five pearl-oyster valves to show the variations in the arrangement 



and number of the scars produced by the insertion of the pallial muscles; nat. size. Lev.a. 



and Lev.p. indicate the scars of the anterior and posterior levators of the foot. 



PLATE V. 



Showing a series of sections across the body at different levels ; slightly enlarged. D, dorsal ; V, ventral ; 



R, right, and L, left side of body. 

 Figs. 1 to 8. Vertical transverse sections in series from before backwards. 

 Fig. 1. Through (esophagus (Oe.) ; anterior end of byssal pouch (By.p.) ; palps (Pa.) ; anterior and 



posterior levator muscles (Lev.a., Lev.p.) ; gonad (Go.) ; mantle lobe (Pall.', Pall.") ; pallial 



edge (Mg.PalL); and velum (Vel.). 

 2. Through anterior part of stomach (St.), parallel with last, showing also digestive gland (D.gl.) 



and hepato-pedal artery (Art.h.p.). 

 3. Parallel with last, through lower part of byssal pouch with byssus-root (By.r.) ; antero-dorsal 



tip of nephridial sac (Neph.) ; end of intestinal loop (Int.lp.) ; and obliquely through 



branchiae (Br.). 

 4. A little posterior to last, showing postero-ventral hepatic duct opening into stomach (St.) ', 



glandular part of nephridium (Neph. 1 ); sections through intestinal loop (Int.lp.); and anterior 



ends of the two retractors (Bet.) joining on posterior wall of byssal gland. 

 ,, 5. Through posterior end of stomach (St.), showing intestine (Int. 1) leaving stomach, the two 



retractor muscles (Ret.) converging towards byssal pouch; nephridial sacs (Neph.) at their 



widest; Adductor muscle (Add.'), &c. 

 ,, 6. In vertical plane immediately behind stomach, along ascending intestine (Int. 2), two portions of 



adductor (Add.' and Add.") ; visceral artery (Art. vis.) descending through gonad, &c. 

 ,, 7. Through the auricles (Au.) and posterior end of visceral mass with rectum (Int. 3); insertion of 



retractors (Bet.); pericardium (Per.); median venous sinus (Sn.m.); and lateral adductor 



sinuses (Sn. add. hit.'). 

 8. Through ventricle (V.) and rectum (Int. 3), upper and posterior part of auricles (Au.), pericardial 



arch (Per.ar.), anterior aorta (Ao.a.), branches of median sinus (Sn.m.'), vV T c. 

 ,, 9. Oblique dorso-ventral section through middle of visceral mass, adductor muscle, &c, as before. 

 Figs. 10 to 14. Horizontal sections at different levels, working downwards. 

 Fig. 10. At level of stomach (St.), showing anterior levators (Lev.a.) in transverse section, palps (Pa.), 



supra-cardial part of rectum (Int. 3), pericardial arch (Per.ar.), and an arrow entering anterior 



aorta cut obliquely. 

 ,, 11. At level of ventricle (/'.) and dorsal part of foot (F.), showing 3 sections of the intestine 



(Int. 1, 2, 3), palps (Pa.), &c. 

 ,, 12. At level of auricles (An.), showing auriculo-ventricular apertures, rectal ridge (B.r.) on 



posterior face of adductor, &c. 

 ,, 13. Through middle of foot, showing origin of retractors (Bet.), inter-auricular communication, &c. 

 ,, 14 Through byssal gland and root of byssus (By.r.), showing course of retractor muscles to 



insertion (Ret. ins.), &c. 



L 



