DIGESTIVE ORGANS. 103 



digestive tract at the stomach ; if a blind sack is present tliey 

 enter in front of it. 



One ma}^ accordingly regard the liver as a much subdivided 

 gland, since it is only at a few places, in respect to minute 

 structure, that its ducts and sinuses may be distinguished from 

 the terminal lobes. The liver consists here, as in all univalve 

 mollusks, of an outer structureless membrane and an internal 

 epithelium of roundish secretive cells, which have a distinct 

 nucleus and yellow concretions, and also contain fat. H. Meckel 

 would distinguish fat and bile cells ; according to Leydig, 

 however, there is no such distinction possible. The hepatic 

 lobules are united together by thin membrane, plexuses of tinely 

 subdivided blood-vessels surround them, and externally the whole 

 liver is surrounded by a blood sinus. 



In the nudibranchiates (xiv, *72), the stomach is remarkably 

 branched, its ramifications even entering the dorsal respiratory 

 papillffi in the Eolids, These ramifications have glandular walls 

 which secrete bile and may therefore be considered a singular 

 sort of liver. Although the intestine is functionally replaced by 

 this anatomical disposition, it still exists in the form of a very 

 short tube opening on the right side of the bod}^ The interpre- 

 tation of the gastro-hepatic organ of the Bolidians has given rise to 

 much discussion. Quatrefages proposed for the Eolis and Elysia 

 the name of Phlebenterata, and supposed that the product of 

 digestion ( chyle) was aerated in the gastric ramifications by the 

 direct influence of the surrounding water. In the former he 

 admitted a heart and arteries but no veins, in the latter he 

 supposed both heart and blood-vessels to be wanting (^phlebs, a 

 vein ; entera, the intestines). He denied an anus to the digestive 

 tube, and thus gave to the hepatic caeca the ofiices of both diges- 

 tion and circulation. The fallacy of all this has been shown by 

 Souleyet, who has demonstrated the existence of heart, veins and 

 anus in the Eolidians. The kidney or renal organ is single in all 

 gastropods (paired in the Scaphopoda and lamellibranchiatesj, 

 and placed in the vicinity of the heart. It is represented hy the 

 Bojanuii organ of the bivalves. 



The kidney is a large, hollow, glandular mass at the base ol^ 

 the respiratory cavity, close to or sometimes perforated (^Triton) 

 by the rectum. It contains a fluid having a whitish or brownish 

 appearance, filled with hard granules, and in which Jacobson first 

 detected the presence of uric acid, ammoniac and salts of lime. 



If the kidney is cut open the internal cavity is observed, which 

 is, however, much narrowed by numerous thick, spongy, crimped 

 annular folds or meshes, which clothe it internally. The spongy 

 walls, the surface of which, because of the folds is much increased, 

 are covered with round cells, which excrete the urinary products. 

 At the wall of the cells, at least in the youngest ones, there is 



