94 CEYLON PEAEL OYSTER REPORT. 



This species is exceedingly rare in the pearl oyster. Four individuals only have 

 been found, two from oysters hailing from the Periya Paar Kerrai, and a like number 

 from the Muttuvaratu. Both of the former were found in the muscular pallial 

 region in front of the base of the foot (Plate IV., fig. 65) in separate oysters. Of the 

 others, one lay in the floor of the visceral mass, the other in the posterior ventral 

 region of the mantle. 



As in Muttua iiiiirijiiritifcrce, the stage met with bad the outward form and the 

 rudiments at least of all the organs of the adult individual. The specimens found 

 were, however, not sexually mature, and being in an encysted condition must be 

 considered as a Cercaria. Their length when in a normal non-contracted condition 

 is |- of an inch (3 millims.). They are of an elongated narrow lanceolate shape, with 

 a ratio of length to breadth of about C> to I (Plate IV., figs. 58 and 59). 



The cuticle is perfectly smooth, without denticles or ornamentation of any 

 description. 



The slickers are of greatly disproportionate size, the ventral rather more than twice 

 the diameter of the oral (ratio of 7 : 3). The former (v.s.) is rendered further con- 

 spicuous by being pedunculate, rising boss-like from just behind the centre of the 

 body. The peduncle is rather longer than half the diameter of the sucker (Plate IV., 

 fig. 58). It has a large degree of mobility. 



When in situ, and also when freed from" its capsule, to the naked eye the worm 

 appears of a pale pink tinge ; under a low power of the microscope this is resolved 

 into a dark yellow coloration confined to the oesophagus and wide digestive cseca 

 of the alimentary canal. The only other colour present, when viewed by trans- 

 mitted light, is the black of the narrow excretory trunks. 



The mouth is situated at the bottom of the funnel-shaped cavity of the oral 

 sucker (Plate IV., fig. 59, o.s.). It opens almost immediately into the short muscular 

 pharynx (/>/>.). A rather wide aperture admits in turn to a peculiar saccate, sub- 

 globular (esophagus (a 7 .) which gives off laterally and dorsally a branch on either 

 side. These pass outwards, at right angles, for a short distance, then, turning 

 posteriorly, they are continued as very wide blind sacs, the digestive caeca (d.c.) as 

 far as the anterior bolder of the excretory vesicle (c.v.). A great mass of yellow 

 granules distends both oesophagus and digestive caeca, imparting a characteristic deep 

 yellow hue to the digestive system. By reason of their great bulk these organs 

 occupy the major portion of the body of this worm a condition contrasting notably 

 with the transparent and practically empty state of the alimentary canal in Muttua 

 margariiifei ce. 



The main trunks of the excretory system (ex.tr.) are two narrow tubes, black by 

 reflected light, coursing backwards in sinuous manner from the pharyngeal region, one 

 on either side. Posteriorly they empty into the slender pyriform excretory vesicle 

 (e.r. ), transparent and contractile. The products of excretion pass to the exterior by a 

 terminal excretory pore (ex.pX 



