74 CEYLON PEARL OYSTER REPORT. 



PLATE VI. 



Fig. 1. General anatomy of the pearl oyster as seen in sagittal section. The alimentary canal is slightly 



diagrammatic, as the limbs of the visceral loop do not lie in one plane, and neither the 



descending nor the ascending parts of the intestine are exactly in the median plane, and 



consequently would not occur in the one section. The size is that of a 2^-year-old oyster. 



For the explanation of the reference letters, see list on p. 70. 

 ,, 2. Dissection (semi-diagrammatic in parts) in same position as last figure, to show the principal 



arteries, see explanation of reference letters on p. 70. 

 ,, 3. Dissection of the alimentary canal ; nat. size. 

 4. Transverse vertical section through dorsal part of visceral mass, passing through posterior part 



of stomach to show the two parts separated by the postero-ventral fold (P.v.f.) and the 



intestinal aperature (Inl.ap.); enlarged. 

 ,, 5. Horizontal section through visceral mass at base of the byssal gland, showing the retractor 



muscle fibres (Fib.ret.) inserted into the wall of the folded byssal gland (F.hy.p.) ; Go., gonad ; 



Art., arteries; Int. 1 and 2, descending and ascending parts of intestine ; enlarged. 

 ,, 6. Stomach bisected horizontally ; roof viewed from below, to show the opening of the oesophagus 



(<i'.) and ducts; enlarged. Stomach wall in solid black. 

 ., 7. Floor of same stomach viewed from above, to show dendritic plate (Pl.d.) and the various 



openings ; enlarged. 

 Diagrammatic longitudinal vertical section of the stomach to the right of the median line, to 



show ducts entering ; enlarged. 

 Diagrammatic longitudinal vertical section of the stomach to the left of the median line, to 



show ducts entering ; enlarged. 

 Outline of cavity of first or descending part of intestine : a, caecum of crystalline style ; b, intes- 

 tinal cavity proper ; enlarged. 

 Portion of second or ascending part of intestine, opened to show the typhlosole (Ty.) ; enlarged. 

 Transverse section through rectal ridge, on posterior surface of adductor muscle, to show rectum 



(a) with its typhlosole (Ty.) ; c, loose connective tissue; /*, posterior aorta (see also Plate IX., 



figs. 6 and 7) ; enlarged. 

 ,, 13. Diagram to show the ciliated paths leading from the gills by the palpar gutters (b) to the 



mouth (a) ; d, channel between base of external gill and mantle ; e, at junction of external 



with internal gills; /, at junction of internal gills; h, along crest of external gill; i, along 



crest of internal gill. The paths diverge, converge, and join as shown. 

 ,, 14. Dissection to show the course of the ciliated track (Pall.al.b.') from labial palp (Pa.) along base 



of velum to pallia] fold (Pall.f.), opposite posterior tips of gills. Ret.palL, pallial retractor 



muscles; Pel., particles ejected; nat. size. 

 ,, 15. Dissection from the right side, with right pallial lobe and right ctenidium removed, in order to 



show the course of the cerebro-visceral connective (C.v.cnn.) ; nat. size. 

 ,, 16. Diagram of the pedal ganglion (Ped.g.) and its connections and nerves; nat. size. 

 ,, 17. Posterior surface of adductor muscle (Add.), showing the parieto-splanchnic ganglia (Par.sp.g.) 



and their nerves; n.br., branchial nerve; n.pal, pallial nerves; n.s.o., nerve to sense-organ 



(S.o.) ; nat. size. 

 ,, IS. Ventral aspect of adductor muscle and visceral mass (r.m.), to show the nerves given off by the 



parieto-splanchnic ganglia ; nat. size. Lettering as in last figure. 



PLATE VII. 



Fig. 1 . Diagram of the heart and pericardium, seen from behind ; enlarged. 

 2. The same from right side. Lettering for both figures : 



An., auricle; /'., ventricle; Per., pericardium; Rn.pei;., reno-pericardial canal; Njj.cuh., 



