278 MR T. J. EVANS ON 



that passes into the integument is much in excess of that, in the Uorids. The thin 

 skin, studded with papillae, is conducive to this amplification of the tegumentary 

 respiration in Bathydoris, while the thick, glandular, and spiculose skin of the Uorids 

 has vitiated this system and necessitated the extension of the special gills. The dorsal 

 wall of the hsemoccele is a membrane more or less bound to the underlying organs by 

 conjunctive-tissue fibres. This membrane is separated from the dorsal integument by 

 an empty space, but runs into it at the side of the body all round. Thus, when an 

 incision is made through the dorsal body- wall, the space entered is not the hremocoele, 

 but this closed cavity between the body-wall and the dorsal wall of the haemoccele. 

 The same arrangement is present in the Dorids alone among Nudibranchs, though the shell- 

 cavity of Pleurobranchus closely resembles the problematic dorsal cavity of the Dorids. 

 Whatever be the nature of the cavity, HANCOCK and EMBLETON'S name peritoneum 

 for its lining should not be perpetuated. The passage of blood from the underlying 

 hsemoccele into the skin and its papillary outgrowths takes place below the level of the 

 edge of the dorsal hsemoccelic wall all round. The blood that runs from the hsemocoele 

 to the gills passes along two narrow conduits on the posterior aspect of the liver (h.v., 

 fig. 10). This must be regarded as of secondary importance in the afferent branchial 

 system. 



(4) The Afferent Branchial System. (Fig. 10.) 



Blood enters the branchiae from two sources : (a) from the hsemocoele by the small 

 paired ducts (h.v.) already mentioned, and (b) from a great median venous space (m.s.) 

 lying above the liver, which receives the blood from the kidney, liver, and gonad. Just 

 before narrowing in order to enter the gills (a.b.v.), it receives the paired ducts from 

 the haemoccele (a). (See also the description of the kidney.) The afferent space at the 

 base of the gills is not a circle, as in the Dorids, but a transverse expansion of the 

 afferent vein from which ramifying tubes run up the branchiae. 



(5) The Efferent Branchials. 



The afferent and efferent venules in the gill-leaflets form continuous loops from the 

 afferent to the efferent side of a gill lobe, and the efferent veins from the two gills join 

 together to form a transverse space at the base of the gills similar to the contiguous 

 afferent space. This space is connected with the auricle by a tube (c.b.v.) running to 

 the right and entering the auricle at its right-hand corner. 



(6) Tlie Efferent Tegumentary System. 



The blood that enters the skin and its papillae from the hsemoccele returns from all 

 sides into a circular sinus (c.s.) running round the edge of the pericardium. The 

 efferent tubules returning blood into the sinus were described by BERGH as renal tubules 

 in B. abyxsorum. The sinus opens behind into the efferent branchial vein just before 



(HOY. soc. EDIN. TRANS., VOL. L., 200.) 



