2G6 CEYLON PEARL OYSTER REPORT. 



Fig. 6. A section through the byssus cavity. The demicanal, d.c, is still apparent, but the whole cavity 

 is lined by a similar ciliated epithelium, m.sp., median septum ; l.sp.\ the thick lateral septa 

 on either side of the demicanal ; l.sp", smaller lateral septa. 



7. A portion of a section through the byssus cavity, somewhat anterior and oblique to the section 

 drawn in fig. 6. The byssus gland cells, By.gk, are seen to be breaking up, and the granular 

 secretum stained red with safranin is passing between the epithelial cells. The granular 

 secretion in the cavity itself is omitted. Zeiss' t V hom. imm. Comp. Oc. 4. 



8. A transverse section through the oesophagus of Jousseaumia heterocyathi. ht.dk., lateral diverticula 

 of the cesophagus, resembling the oesophageal pouches of Protobranchia. Zeiss' -~ hom. imm. 

 Comp. Oc. 4. 



PLATE II. 



Figs. 9 to 19. A series of transverse sections through Jousseaumia heteropsammice. Fig. 9 passes through 

 the cerebral ganglia and fig. 19 through the visceral ganglion pair. All the figures are fully 

 lettered. 



PLATE III. 



Fig. 20. A section through the ventral end of the demibranch of an immature individual of ./. hetero- 

 psammice. Zeiss' t V hom. imm. Comp. Oc. 4. 

 ,, 21. A section through two adjacent gill filaments of a mature individual of ./. heteropsammice, 



showing the interfilamentar junctions. 

 22. Optical sections of two gill filaments of /. heterocyathi. A represents the filaments as seen with 

 a high focus, and shows the latero-frontal cilia, /./., borne on columnar cells. B represents a 

 section as seen with a somewhat deeper focus, and shows the lateral cilia, /., borne on the 

 large oblong cells, I.e. C, taken at a still deeper focus, shows the interfilamentar junctions, 

 which are occasionally double, as in the centre of the figure, and the cells x, which give rise to 

 the outgrowths forming the junctions. 



A diagram showing the relations of the kidney, pericardium, and gonads in Jousseaumia, from a 

 reconstruction of a series of sagittal sections. 



A horizontal section through the gonaducts, vesiculse seminales, and posterior part of the kidney 

 of J. heteropsammice. Zeiss' t V hom. imm. Comp. Oc. 4. Con., renal concretions. 



A section somewhat lower down from the same series as fig. 24, showing the renal duct, Re.d., 

 and the opening of the vesicula seminalis into the gonaduct; !:, attachment of branchial 

 filament to the body-wall. 



A section next but one in the series to that shown in fig. 25, showing the renal (Be.a.) and 

 genital (Go.a.) apertures. 



A young individual of ./. heterocyathi with one growth lamella outside the prodissoconch, and 

 with five gill fenestrations and the commencement of a sixth ; pr.diss., outline of the pro- 

 dissoconch ; Card. a., anterior cardinal hinge tooth, x 150. 

 ,, 28. A somewhat older individual of the same species with seven gill fenestrations and four growth 

 lamella? outside the prodissoconch. x 150. 



