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THE AMERICAN NATURALIST [Vol.XLIV 



the young animal gets its food, or a portion of it, by means of a sort 

 of proboscis, or elongation of the mouth part, which is capable of being 

 moved about freely within the shell cavity. This proboscis stage lasts 

 until the gills are fully formed and becomes of sufficient size to supply 

 food to the animal, when the proboscis, or rather its flexible end, is 

 transformed into the labial palps which become closely connected with 



The mouth narrows down into an oesophageal tube of 

 transversely elliptical calibre, lined by cells similar to 

 those of the mouth. It is still relatively long and curves 

 over the anterior end of the stomach, passes between the 

 lateral origins of the liver, and enters the stomach from 

 above (Figs. 2-10). The stomach is a relatively large 

 mass of irregular shape and large cavity, occupying a 

 good part of the space in the prodissoconch. There may 

 be considered to be three prominent extensions : one for- 

 wards below the oesophagus, another postero-dorsal be- 

 hind the entrance of the oesophagus, and a third, begin- 

 ning as a compressed ventral extension of the first, slants 

 downwards and backwards towards the adductor muscle, 

 becoming broad, deep, regular and thick-walled. This, 

 I am satisfied, is the portion that secretes the crystalline 

 style, and originates postero-dorsally in the left umbo 

 of the larva, but becomes moved to its present position 

 during the rotation of the viscera, and presents the ap- 

 pearance of being internally ciliated. Just in front of 

 the insertion of the oesophagus but on each side of it, 

 i. e., dorso-laterally, spring the stalks of the liver— one 

 on the left and two on the right. These branch into 

 numerous follicles lying on both sides of and above the 

 stomach and projecting far forwards to the region of the 

 mouth. On the ventral aspect of the stomach, in the 

 same region, springs the intestine, on the right, in the 

 crease between the compressed antero-ventral extension 

 to the left and the main central body of the stomach 

 above (Fig. 9). From this the intestine passes back- 

 wards on the right, then upwards behind the rounded 

 postero-dorsal extension, forwards and down the left 

 side, where, near the anterior end of the stomach it turns 



