256 CEYLON PEARL OYSTER REPORT. 



kidneys of Lyonsiella abyssicola and L. norvegica figured by PELSENEER (11). The 

 median sac formed by the fusion of the right and left kidney sacs in Jousseaumia lies 

 just in front of and above the posterior retractor pedis muscle, near where the latter 

 bifurcates to be attached to the right and left valves of the shell. The two posterior 

 horns of the sac are of considerable length, and extend along the outer sides of the 

 diverging bundles of the retractor pedis muscle, extending blindly just below the 

 anterior end of the posterior adductor muscle. The anterior horns of the sac are 

 smaller and pass to the outside of the retractor pedis muscle. The median sac and 

 its anterior and posterior prolongations are lined throughout by a thick vacuolated 

 layer of protoplasm containing relatively large oval nuclei, but I was unable to 

 distinguish any cell outlines. The renal concretions lie in the vacuoles and are 

 similar to those described and figured by PELSENEER (11). The relations of the renal 

 ducts and the reno-pericardial canals are shown in fig. 23, and the renal ducts are 

 shown in section in figs. 25 and 26, Re.d. They are short canals lined by a cubical 

 ciliated epithelium and open into the supra-branchial cavity, in close contiguity to 

 the genital apertures, on a small papilla situated to the outside of the visceral 

 commissure. The reno-pericardial ducts are very minute, and it was difficult to 

 discover them even with the aid of the highest powers of the microscope. They are 

 extremely fine ciliated ducts opening into the floor of the renal sac not far in front 

 of the uroducts. Each reno-pericardial duct runs forward close below the external 

 part of the floor of the median renal sac, and, passing to the inside of the uroduct, 

 turns upwards and opens by a minute ciliated aperture into the pericardial cavity. 



THE NERVOUS SYSTEM. This is of the usual lamellibranchiate type, and presents 

 few features of interest. The nerve ganglia are relatively of great size, as may be 

 seen in figs. 9, 12, and 19. Their proportions, relatively to the whole size of the 

 animal, may be described as larval, and this, coupled with the fact mentioned below 

 (p. 257), suggests that the sexual products in Jousseaumia are precociously developed, 

 and that we have, in fact, an example of paedogenesis. In the cerebro-pleural ganglia 

 the separate groups of nerve ganglion cells forming the cerebral and pleural moieties 

 of the ganglia are easily recognisable, but the cerebro-pedal and pleuro-pedal 

 connectives leave the fused ganglia as a single nerve. The otocysts are situated above 

 the hinder part of the large nerve mass formed by the fused pedal ganglia, and are 

 quite separate from the ganglia and contained in special compartments of the general 

 body-cavity or haemocele (fig. 13, ot.). Each otocyst contains a single large otolith. 

 The visceral ganglia are of great relative size, and the posterior pallial nerves are very 

 stout. I was unable to find any trace of an osphradium in the form of a specialised 

 patch of epithelium in the neighbourhood of the visceral ganglia, or on the course of 

 the posterior branchial nerves. 



THE GONADS AND GONADUCTS. Jousseaumia is monoecious, and, as is usual among 

 hermaphrodite lamellibranchia, is protaudric. By far the greater number of the 

 individuals examined by me contained spermatozoa only, but in some few both ripe 



