﻿80 PROCEEDINGS OF THE NATIONAL MUSEUM vou 102 



need fee removed for gross examination or sectioning, but occasion may 

 demand search in other organs in studies concerning the migratory 

 paths of entering miricidia or escaping cercariae. Attention is drawn 

 to the section on parasitology (p. 108). 



The animal is held within in its protective shell by the strong, curved 

 columellar muscle running posteriorly from the opercular region of 

 the foot and curving around the inner columella. In material that has 

 been preserved in formalin or 70 percent alcohol the columellar muscle 

 loses its strength of attaclmient to the shell, and animals are usually 

 easily drawn from their shell with the aid of a bent pin or sharp, curved 

 probe. It is impossible to extract the animal of living specimens with- 

 out seriously rupturing most of the organs. The shell must be cracked 

 and picked away from the region of the penultimate whorl (the whorl 

 above the aperture) to expose the area where the muscle is attached 

 to the columella. A dissecting pin may be used to scrape away the 

 attaching fibers. Living material has the additional disadvantage of 

 becoming sticky from the exudation of mucus. However, certain 

 organs are more easily found and studied in fresh material than in 

 preserved specimens. 



The general position of organs is shown in figure 33, A. The most 

 conspicuous and most easily found organ is the "liver," or digestive 

 gland, which in preserved material is a sandy brown and in fresh ma- 

 terial is darkish green with numerous, small, embedded black spots. 

 The digestive gland usually occupies the apical or top two or three 

 whorls. Embedded in the columellar side or inside of the coil is the 

 small, tubular-shaped gonad. Just below the digestive gland is found 

 the rather large stomach, which may be easily found by tracing back 

 along the easily seen feces-packed intestine. Between the stomach 

 and the lower part of the intestine may be found the oval-shaped, sac- 

 like kidney, which is conspicuous in its possession of internal fleshy 

 septa or lamellae. Lying beside the kidney, and also just anterior to 

 the stomach, is the pericardial sac, which contains the single auricle 

 and one ventricle. The position of the heart may also be found by 

 following back along the ctenidium, which arises at the base of the 

 auricle. The esophagus is usually thin walled, small, and difficult to 

 find at first, but may be more easily located at the point of its juncture 

 with the posterior end of the stomach or where it emerges from between 

 the brood pouch and the columellar muscle. 



ALIMENTARY SYSTEM 

 FiGUBES 34-36 



Pharyngeal region : The mouth is a vertical, narrow slit located 

 at the anterior end of the proboscis. It and the two labial pads 

 that flank it on either side face slightly ventrally. The oral 



