770 PROF. G. C. BOURXE ON THE 



lined throughout bv a glanJuhir epithelium, consisting, as far as 

 I was able to detevniine, almost -wholly of very long goblet-shaped 

 secretory cells containing zymogen granules, with very few attenu- 

 ated supporting cells lying between. The histological chai-acters 

 of the epithelium were not, however, very well preserved in any 

 of my specimens. The two pouches are closely pressed against 

 the sides of the cesophagus, and in the species in which they are 

 longest follow the turns of the latter. Hence, as the oesophagus 

 makes a turn towards the left before it passes down through the 

 loop of the rectum, the right oesophageal pouch generally passes 

 over to the left side and above the a?sophagus, the left pouch 

 passing to the right and below the cesophagus and radular sac. 

 The oesophageal pouches are relatively short in Alcadia paUiata 

 and of appi'osimately equal width throughout, but they are much 

 longer anol oiiminish in diameter towards their posterior extre- 

 mities in A. koUandi. They are particulai4y long anoi of a deep 

 chocoilate colour in Palceohelieina idee ; in most species they are 

 white in spirit-specimens. 



Behinol the openings of the oesophageal pouches the oesophagus 

 narrows somewhat abruptly in diameter ; the glanolular internal 

 longitnoiinal riolges disappear, anol are replaceol by nine or ten 

 longituoiinal ridges formeoi by columnar ciliated epithelial cells, 

 and these may be traced throughout its coui'se to the stomach. 

 This course is a long one, for the stomach lies aslant on the 

 lower side of the viscei-al mass, below the greater part of the 

 lobes of the liver and below the coils of* the intestine. As seen 

 from above and behind, it is a large pyriform sac, the narrower 

 end lying just above the posterior corner of the pericardium ; 

 the broader end forming on the right side of the visceral mass a 

 large rounoled prominence which fits into the concavity on the 

 ventral siole of the i-ight columellar muscle. The oesophagus 

 enters the stomach on the upper side o^f its broader end. anol its 

 course in the several species examineol will be hiest unolerstoooi by 

 reference to PL XXXII. figs. 10 to 15. Passing to the left as it 

 enters the visceral mass, the oesophagus lies above the first coils 

 of the rectum, then passes below the recurrent coil of the rectum, 

 and so arriving at the oiorsal surface of the stomach runs along 

 the latter as a flattened tube anol opens, as stated above, into 

 its broaoier end, oiUating considerably just at its point of entrance. 

 This dilatation, which might almost be described as a diver- 

 ticulum of the stomach itself, receives right and left the wide 

 oiucts of the liver (PL XXXI. fig. 7, and PL XXXII. fig. 16. li.d.). 



The internal structure of the stomach is very complicated. It 

 attracted the attention of Isenkrahe. who gave a fairly accurate 

 description of it. Fig. 7 is a representation of a dissection of the 

 stomach maole from behind anol below the visceral mass. The 

 cesophagus is shown at ce., and its entrance into the stomach is 

 indicated by the aiTow. The entrance of the left liver-duct is 

 shown at li.d. ; that of the right liver-oluct lies on the far siole 

 ©f the prominent curved ridge guarding the entrance to the 



