10 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



nearly to the anterior adductor muscle, then turns dorsally and 

 posteriorly, gradually assumes a medium position again, passes through 

 the ventricle, and opens into the mantle chamber at the base of the 

 exhalent siphon, just behind the posterior adductor muscle. The 

 intestinal epithelium is composed of short, deeply staining cells, which 

 are frequently arranged in longitudinal ridges. 



DIGESTIVE GLANDS. 



The racemose digestive glands open into the stomach near its dorsal 

 end by short broad ducts. The lobes are very numerous and form a 

 rather compact mass in the dorsal region of the body, which latterly 

 overhangs the dorsal part of the foot. The left gland is larger than the 

 right. 



LABIAL PALPS. 

 FIGURES 3 AND 5, Ip. 



The palps of the adult animal are very large, Fig. 3, Ip. Each 

 united pair is suspended from the body wall by a thin membrane, 

 which contains a few muscle fibres. This membrane is attached to the 

 body wall beneath the overhanging digestive gland. The palps are 

 triangular in shape and have their inner surfaces ciliated and thrown 

 into series of ridges and grooves that do not extend quite to their free 

 margins. Large blood-spaces follow along the bases of many of these 

 ridges. The supposition that the large expanded palps serve in 

 respiration seems probable. 



Each outer palp is supplied with a long appendage, Fig. 3, pap., 

 which originates from its posterior end, near its dorsal margin, and 

 can be extended far beyond the posterior margin of the shell. 



In young specimens, this appendage is flat and is entirely confined 

 to the external palp, Fig. 5, pap. As it grows it folds longitudinally, 

 so as to form a groove on its inner side, and, at the time, twists so 

 that it may appear like a continuation of the united dorsal margins 

 of the outer and inner palps. 



Each palp-appendage is supplied with longitudinal muscles, Fig. 

 18, 1m., a large nerve, pn., that is continued into it from the dorsal 

 margins of the palps, and a continuous blood-space, bs., lying beside, 



