MOLGULA. 39 



they bulge, rolled in a fold of the lining membrane. 

 The oral orifice is large and circular, and opens into the 

 base of the branchial sac close to the ventral margin. 

 The oesophagus is a short, ill-defined tube, which 

 gradually enlarges backwards as it merges into the 

 stomach ; this is a mere irregular enlargement of the 



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alimentary tube, and is somewhat elongated ; it is of 

 no great size, and as it passes downwards it bends 

 backwards and graduates into the intestine, which is a 

 large, pretty-equal tube, that runs across nearly as far 

 as the endostyle at the opposite or dorsal margin of 

 the body ; it then ascends, and, doubling upon itself, 

 forms a transverse loop ; after this it again ascends 

 and reaches the atrium just above the point where the 

 oesophagus penetrates the respiratory organ. There it 

 terminates in a wide anal orifice with a slightly- 

 reflected rim which is broken at the side next the 

 branchial sac. 



The liver, in this genus, is a well-developed organ. 

 It is usually of a dark green colour, and overlies the 

 stomach, concealing* entirely its inner or right side, 

 and very much obscuring its general form. It is an 

 irregularly-lobulated mass AY Inch appears to be made 

 up of wide laminas closely pressed together and more 

 or less confused and involved. This is the appearance 

 of the hepatic organ in M. conckilega ; but in M. com- 

 planata the laminge and lobes are very distinct, and the 

 mass has very much the appearance of a folliculated 

 and lobed sac. 



The dio-estive oro-ans do not vary much in the 



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different species. In M. simplex the intestine is much 

 elongated, and passes from one margin of the body to 

 the other, the looped portion being turned upwards 

 and forwards so as to pass above the reproductive 

 organs, and the margin of the anal orifice being denti- 

 culated and reflected. There are consequently two 

 distinct loops in this species, an upper and a lower 

 loop. In M. inconspicua the intestine is still more 

 extensively developed, the upper loop being wide, and, 



