ON THE STRUCTURE OP .TINIGMA ^NIGMATICA. 267 



across the body and attached to what is morphologically the 

 left side of the foot. 



The Alimentaey Tract. 



The mouth leads into a narrow, and, for a Lamellibranch, 

 relatively long, oesophagus, lined by a ciliated glandular 

 epithelium, whose characters will be described in the latter 

 part of this paper. The oesophagus passes into a capacious 

 stomach occupying the greater part of the visceral mass 

 dorsad of the foot. The roof of the stomach is thin, and 

 lined by a few ciliated but non-glandular columnar epithe- 

 lium, which extends down for some distance on the riglit 

 wall, especially in the anterior half of the stomach. The 

 right wall and floor, and in the posterior half of the stomach, 

 the left wall are, on the contrary, lined by an epithelium 

 consisting of very long attenuated ciliated cells, intermixed 

 with whicli are numerous elongated claviform gland-cells 

 filled with yellow granules. The floor of the stomach is also 

 thrown into longitudinal folds, and is covered by a thick 

 cuticular layer, the "fleche tricuspide" of Poli, whicli is 

 apparently secreted by the yellow gland-cells. This question 

 will be discussed more fully in the latter part of this paper. 

 The stomach is embedded in the liver, which opens into it 

 by several large ducts. One of these ducts is dorsal, and 

 communicates with the superior lobe of the liver; the 

 remainder are posterior and ventral, and some of them run 

 far back in the posterior mass of the liver before breaking 

 up into branches (figs. 9 and 10, U. d.). Posteriorly the 

 stomach presents a dorsal cascum, into which one of the 

 largest of the posterior liver ducts opens. Ventrally it 

 narrows in diameter, and gives ofi: the intestine and sac of 

 the crystalline style. 



The intestine opens into the stomach by an aperture 

 common to itself and the sac of the crystalline style. The 

 entrance to the intestine is guarded by a number of promi- 



