OF MASSACHUSETTS. 17 



organs are the labial palps (lp), which correspond to the lips of 

 higher animals and function in conducting the food to the mouth. The 

 central portion of these lips, which extend laterally for a distance equal 

 to the thickness of the animal near the umbo, has arbor-vita3-like proc- 

 esses, concealing the mouth. The flaps which extend on each side of 

 the branching area are united to the body dorsally and posteriorly, 

 leaving the other edges free. The exterior surface is smooth, while the 

 internal surface is covered with ciliated ridges and furrows which aid 

 in conducting the food from the gills to the mouth. 



Digestive System. The digestive system of the scallop is compara- 

 tively simple. The mouth opens into a short oesophagus or gullet, which 

 leads into a gourd-shaped stomach (s). On the posterior end of the 

 stomach is a curious hard socket into which fits the tip of a translucent 

 gelatinous rod, the crystalline style. This rod extends along the in- 

 testine in a sort of pocket or groove as far as the lower part of the 

 visceral mass (Fig. 75, vm). The stomach is enveloped by a dark-brown 

 mass, connected with it by two short canals, one on each side. This 

 large conspicuous organ is the digestive gland or "liver" (1), and "is 

 only bounded in the region of the stomach by the sexual gland on its 

 ventral surface." Kellogg (6). The liver (1) sends secretions into the 

 stomach to aid digestion. The food is caught up as soon as it leaves the 

 stomach by the cilia of the intestine (i), which forms a double loop in 

 the visceral mass (Fig. 76, vm). It then passes in a dorsal direction 

 through the liver, curving posteriorly to pass through the heart, and 

 finally ends posterior to the ventral portion of the adductor muscle. 



Circulatory System. The scallop has a blood system passing over 

 the whole body and through the gill filaments, where the blood' is 

 aerated. The heart (ht), a three-chambered organ, is situated in a 

 pericardial cavity dorsal to the adductor muscle. The intestine passes 

 through the pericardium and is surrounded by the ventricle of the 

 heart. The auricles are two filmy bodies connected with the ventricle. 

 From the heart arise the different arteries which conduct the blood to 

 all parts of the body, whence it is returned through the venous system 

 to the sinus venosus, from there to the gills, and finally back to the 

 heart. 



Nervous System. The nervous system of the scallop is complicated, 

 and the animal is highly sensitive in all parts, especially in the region of 

 the mantle, through the circumference of which passes a large nerve 

 connecting with the tentacles and eyes. Several ganglia lie in the region 

 of the mouth, foot and visceral mass. From these, numerous nerves 

 pass to the various parts of the body. 



Excretory System The kidneys are a pair of yellow-colored organs 



in the form of sacs, encircling the anterior part of the adductor muscle. 

 These glandular organs open into the mantle chamber above the gills, 

 where they are joined by the openings of the reproductive organs. 



