230 



Scientific Proceedings, Royal Dublin Society. 



from the level of the fifth shell- plate to its posterior termination it 

 is devoid of them. On reaching the hinder border of the bladder- 

 like dilation of the kidney duct first described, it runs outwards and 

 then forwards, in close contact with the dorsal side of the lateral 

 nerve cord. At the level of the penultimate gill it opens by a small 

 pore into the pericardium, beneath the anterior part of the auricle. 



Fig. 2. 



A diagrammatic representation of a transverse section through Chiton discrepans 

 at the level of the renal orifices. The dorsally situated pericardial cavity is separated 

 from the general hody cavity hy the pericardial floor. The posterior, apparently 

 median unpaired part of the kidney, seen by von Jhering, lies on the floor of the 

 general body cavity. A little in front of this section the kidney tubules take up a 

 distinctly lateral position. 



D, p.ff., b.r., Jc.t., r.o., as in Fig. 1 ; A, auricle ; A. C, alimentary canal; b.a., 

 branchial artery ; 5. «>., branchial vein ; 5. c, body cavity ; F, foot ; g.g., generative 

 gland ; Jc. c, opening of kidney tubules into dilated part of kidney duct ; l.n., lateral 

 nerve cord ; ^. w., pedal nerve cord ; ^. c, pericardium; j?. ^-. «?., part of kidney duct 

 which is hidden from view by D in Fig. 1 ; V, ventricle. 



The recurrent internal kidney duct, which receives no glandular 

 cseca, is, with the exception of a small portion adjoining the peri- 

 cardial opening, lined by columnar cells containing a brownish- 

 yellow colouring matter, which renders this portion of the duct 

 easily visible to the naked eye. The part of the duct which runs 

 forwards from the level of the hinder edge of the bladder to the 



