66 OKHAMANDAL MARINE ZOOLOGY REPORT 



is dorsal and posterior, narrow and caecal in appearance and reaches a higher level 

 dorsally ; the third is posterior and the fourth ventral and pyloric. The two latter 

 chambers are very distinctly defined ; the posterior one, which may be termed the 

 biliary chamber, is a deep branched crypt pushing its branches deep into the 

 substance of the digestive gland from which it receives numerous large bile ducts. 

 In the floor of the pyloric chamber two openings of about equal size are discernible ; 

 the one leads into the intestine, the other into the pyloric caecum (C.st.c.). From 

 the latter opening the conical proximal end of the crystalline style (C.st.) projects 

 some distance into the stomach ; a bolus-like mass of partially digested material 

 may often be seen agglutinated upon this stylar projection. 



This cameration of the stomach has the effect of considerably increasing the 

 surface area ; in Placuna the stomach appears to be developed at the expense 

 of the intestine. 



The whole of the stomach is lined with ciliated epithelium, exhibiting great 

 variability in the height of the cells. Usually these cells reach their greatest 

 development on and over the permanent ridges. A delicate and easily detachable 

 gelatinous layer the fleche tricuspide (fig. 23, Fl.tri.} invests a great part of 

 the stomach wall ; wherever this layer is well developed, there we find the epithelium 

 oreatly elongated. This peculiar investment is particularly thick over the central 

 anterior wall of the stomach, where it is intermittently adherent, dipping down 

 between the ridges and pads which corrugate the inner surface of the stomach. 

 No structure save a slight lamination can be detected ; it is perfectly clear and 

 colourless from its behaviour under reagents it appears closely related in composition 

 to the crystalline style. 



The stomach is almost entirely surrounded by the digestive gland. Only over the 

 right aspect and at the extreme dorsal extremity does the investment fail ; in these 

 regions, owing to the laterally compressed form of the animal, the wall of the stomach 

 is separated from the mantle only by thin discontinuous patches of glandular tissue. 



The "liver," or digestive gland (D.gl.), is a large, dense, acinose gland of sage- 

 oreen colour, forming the greater part of the tissues of the visceral mass and forming a 

 nearly complete investment to the stomach, oesophagus, and the proximal half of the 

 intestine. Superficially, a considerable portion is covered in its turn by a thin sheet 

 of reproductive tissue. 



Bile ducts emptying the secretion of the digestive gland into the stomach are 

 numerous (fig. 29, D.gl.d.). At least eight terminal ducts can be traced ; they are the 

 following : 



(a) The dorsal duct opening high up in the postero-dorsal chamber. 



(b) The anterior duct leading from the anterior region of the liver into the 



antero-dorsal chamber ; and 



