BRITISH NUDIBRANCHIATE MOLLUSCA. 13 



noticed, an anterior stomach or crop, formed by a dilatation of the oesophagus. The most re- 

 markable modification of the gastric organ is found in Scyllcea, where it is armed with a belt 

 of horny plates or teeth. A similar armature of the stomach is not, as far as we are aware, to 

 be met with in any other Nudibranch. 



The intestine is always short — in some of the Eolididce excessively so, never convoluted, 

 and, in the Borididce, terminates in an anal opening, on the medio-dorsal line, in the centre of 

 the branchial circle. In the Tritoniadce, and in many of the Eolididce, the vent is on the right 

 side. It is situated on the medio-dorsal line in Antiopa, Proctonotus, Alderia, TIermcea, and 

 Stiliger; in the three former, towards the posterior extremity, in the two latter, far forward in 

 front of the heart. In some others of the Eolididce it is latero-dorsal. 



The liver presents two great types of form. In the Borididce and Tritoniadce it is entire 

 (excepting in Scyttcea, where it is broken up into six or seven globular masses), occupying its 

 normal abdominal position ; in the Eolididce it is more or less diffused. In those genera with 

 an entire liver, it is very bulky, pouring the hepatic fluid into the stomach by one or several 

 large ducts. When the gastric organ is free, as in D. tuberculata, it receives only one duct ; 

 but in those species with the stomach buried in the liver, the bile enters through several large 

 openings in its under surface. In Scyllcea pelagica, and Boris tuberculata, the biliary secretion 

 enters at the cardiac extremity of the stomach : in Tritonia Hombergii, at the pyloric. 



The diffusion of the liver is first seen in Tet/iys* but in it the great bulk of the hepatic 

 organ is still found in the abdominal cavity ; and the gastro-hepatic system is only' in a rudi- 

 mentary state, though developed distinctly on the plan of that of Eolis. Lateral vessels are 

 given off from the stomach and liver, which pass to, and seem to penetrate, the papilla? on the 

 sides of the back between the branchial tufts. In the greater number of the Eolididce, however, 

 the liver has entirely disappeared from the abdomen, and is broken up into numerous minute 

 portions or glands which are thrust into the branchial papillae. The delicate ducts from these 

 glands pass inwards and unite to form great hepatic ducts or trunk channels, which open into 

 the stomach. In the Proctonotince, Glaucince, and Eolidince, there are three such trunk-chan- 

 nels, two lateral and anterior,— one central and posterior : in the last-named sub-family the 

 posterior duct lies above the ovary ; in the two others, below it, shewing, in this respect, their 

 relationship to the Borididce and Tritoniadce, in both of which the ovary overlies the liver. 

 The HermceincB have four great gastro-hepatic ducts, all of which are lateral, — two being ante- 

 rior and two posterior. The great ducts, and the numerous branches leading to them from the 

 glands of the papillae, form the gastro-vascular system of M. Milne Edwards, and M. de 

 Q-uatrefages. 



The gland of each papilla has appended to its extremity an ovate vesicle, which commu- 

 nicates externally by a minute orifice at the apex of the respiratory organ. This vesicle, 

 which has been observed only in Eolis, has the power of discharging filamentous urticating 

 bodies. 



* In the account of Scyllcea, under the head of the genus, we have described a series of vessels 

 or tubes passing from the hepatic globular masses to the skin and branchial tufts ; these we deemed at 

 the time to represent, in a rudimentary form, the gastro-hepatic system of the Eolididce, but we are 

 now inclined to consider them as veins, carrying blood from the biliary organ to the aerating surface, 

 and therefore of the same nature as the hepatic veins in Tritonia, and as the great hepatic trunk vein 

 in Doris. 



