198 MR T. J. EVANS ON 



supply of the kidney is therefore purely arterial, and all the renal arteries arise from 

 an aortic bulb (a.e.) opening into the ventricle at the point o.v. in fig. 8, and continu- 

 ing forwards as the cephalic artery (cart). The extensions of the renal arteries into 

 the gonad are not shown in fig. 8. The blood delivered by the renal arteries — which, 

 as we have seen, occupy the crests of the glandular folds — passes on into A^enous lacunae 

 which lie deeper in the substance of the folds, and open into a great median venous 

 space, lying between the kidney and liver behind, and between the gonad and liver in 

 front. Into this median venous space also passes the blood that has traversed the 

 gonad and liver. 



The main collecting reservoir of the kidney lies behind the gonad, and in its hinder 

 wall is seen the opening into the renal duct which leads to the exterior. In it 

 originates the reno-pericardial duct (r.p.d.), consisting of a median tube opening in 

 front by a funnel into the renal chamber, and a renal syrinx (r.s.) opening on the floor 

 of the pericardium. The syrinx is a bulbous structure with a wide lumen which is 

 almost filled with delicate laminate ingrowths of the epithelial lining. Sections of the 

 floor of the kidney show that the gland cells lying in connection with the renal arteries 

 contain concretions, often of large size, which stain faintly with basic dyes. The con- 

 cretions collect in big vacuoles, which finally burst and liberate the excreted contents. 

 The foliations of the wall of the syrinx are covered with cells of two kinds. The distal 

 part of a lamina — namely, the free edge towards the middle of the lumen — is covered 

 by ciliated cells only, the cilia being extremely long. The proximal part — namely, that 

 nearer the wall of the syrinx — is glandular, and the cells contain fine granules of a 

 substance which takes acid dyes. These cells are continued on to the wall of the 

 pericardium. The renal organ of Bathydoris and its vascular supply are thus Dorid 

 in type, the reno-pericardial duct, especially, being almost identical in structure with 

 its homologue in Doris. The association with the blood glands, non-functional though 

 that may be, the absence of ramifications into underlying organs, and its forward 

 extension into the head region are features not paralleled among true Dorids. 



The Vascular System. (Figs. 9 and 10.) 



In general, the vascular system of Bathydoris resembles that of the Dorids, but in 

 several respects distinct affinities with the blood system of the Pleurobranchids are 

 exhibited. It may be conveniently described under the following heads : — 



(1) The Heart. 



The most obvious feature of the heart and pericardium is their asymmetrical 

 disposition, since the an tero- posterior axis, unlike that of the true Dorids, lies at an 

 angle to the long axis of the body. The pericardium is a spacious cavity lying 

 posteriorly on the surface of the kidney, with the reno-pericardial opening in its 

 extreme right-hand corner. 



