42 CEYLON PEARL OYSTER REPORT. 



GENERAL ANATOMY. 



Before describing the different systems of the body in detail, it may be well to 

 refer to a few of the figures on the plates, which give some idea of the general 

 structure and arrangement of the soft parts of the animal inside the shell. 



Fie-. 3 on Plate II. shows the left side of the animal when one valve of the shell 

 has been removed ; the dorsal surface is above and the anterior end to the left. In 

 the centre is seen the single great adductor muscle (white) with the heart and viscera 

 above it, the sickle-shaped gills (dark) curving round the lower central surface of the 

 muscle, and the foot (at the base of the gills) with its byssus fibres projecting 

 anteriorly (to the left). The mouth is above the byssus, and the anus on the ventro- 

 posterior edge of the muscle where the anal funnel can be seen projecting (right-hand 

 side of figure). 



The three widely gaping specimens seen in fig. 5, a, b, c, show the adductor muscle 

 in the middle crossing from valve to valve, the gills in the form of two lamellae on 

 each side and a mantle lobe or pallium lining each valve of the shell. The pigmented 

 mantle-edge, studded with little papillae or tentacles, is well seen in the left-hand 

 specimen (a). 



The diagrammatic dissections shown in tigs. 1 and 2 on Plate VI. give the chief 

 systems of the body in their relative positions. Fig. 1 shows mainly the course of 

 the alimentary canal from the mouth (0) to the stomach (St.) and through the various 

 parts of the intestine to the anus (at An.f.). Fig. 2 shows, in addition, the heart 

 (Au. and V.) and the principal blood-vessels. The lettering of these figures in the 

 Explanation of Plates will supply further information. 



Finally, the series of sections through different parts of the body, given in Plate V., 

 show the relations of gills to mantle lobes, of gills to foot, of adductor muscle to 

 viscera, of stomach to liver, of intestine to heart, and so on. They need not be 

 described here in detail, as a full account of each is given in the Explanation of 

 the Plates. 



PALLIUM OR MANTLE. 



The integument or outer part of the body-wall forms two great lateral flaps, the 

 right and left pallial or mantle lobes which line the valves of the shell and wall-in 

 the pallial cavity the space, freely open to the water when the shell gapes, into 

 which the foot and the gills project (see the top row of sections on Plate V.). The 

 two pallial lobes are separated anteriorly, ventrally, and posteriorly, but become 

 continuous dorsally underneath the hinge-line of the shell. The free edge of the lobes 

 is thickened, pigmented, and fringed with short branched tentacles (see Plate III., 

 figs. 6 to 10). This pallial edge of the mantle is attached some little distance inside 

 the margin of the shell, and the nacre stops short where the mantle is attached (see 

 Plate II., fig. 6, where the mantle has been drawn back at one point to show the 



