SEA MUSSEL MYTILUS EDULIS. 1 47 



convert it into reducible sugar in about 3 hours, and if a solution of 7 styles in distilled 

 water was added to 30 minims of the same starch solution it was transformed into a 

 reducible sugar in about 20 minutes. Mitra concludes therefore that the crystalline 

 style contains an amylolytic ferment. It acts upon raw starch and is able to con- 

 vert glycogen slowly into sugar but appears to have no action on such protein matters 

 as egg albumin, fibrin, or muscle fibers. He considers the protein matter (globulin) of 

 the style and the ferment as identical substances and believes that the former in no 

 way functions as a reserve food mass. 



The conclusion to be drawn from the investigations recorded above is that the 

 crystalline style originates from the tall columnar epithelium of the direct intestine and 

 gradually moves forward with a spiral motion to the stomach, where it mixes with food 

 and functions as a digestive ferment of starchy materials. 



The experiments of List (1902) on the function of the liver show that the granular 



bodies in the liver cells take up nourishing materials (also carmine, india ink, iron, and 



litmus) in the form of very small particles until the granules are entirely filled; then the 



food materials emerge in the form of large particles which are removed by way of the 



main liver canals to the stomach and intestine. He demonstrated clearly that the 



characteristic color of the liver always depends upon the nature of the nourishment 



taken by the animal and concludes that the liver functions primarily as a storehouse of 



reserve food material. 



CIRCULATORY SYSTEM. 



HEART. 



The heart lies in the mid-dorsal region just posterior to the upper extremity of the 

 hinge where it is inclosed in a spacious pericardial cavity the walls of which are formed of 

 a thin, transparent membrane that is continuous with the body wall (fig. 133, PC, p. 149). 

 The floor of the pericardial cavity rests on the direct and recurrent intestines which run 

 parallel to each other in this region. Laterally it is covered with a thin portion of the 

 mantle that is usually free from any proliferations of the genital epithelium, while dor- 

 sally it is inclosed between the two bands of pallial muscles which are continuous with 

 the mantle edge. In a mussel 8 cm. long the floor of the pericardial chamber is about 

 15 mm. long by 8 mm. wide, and the roof of the cavity which is shaped like an inverted 

 V is about 5 mm. high. At the anterior extremity of its base the pericardial cavity 

 opens into a wide duct that borders the anterior surface of the oblique vein and connects 

 with the kidney. This wide duct was given the name couloir by Sabatier (1877) but 

 may better be called the renipericardial canal (fig. 133, RC). 



The heart is composed of a ventricle and two auricles. The ventricle is more or 

 less elliptical in form and extends the whole length of the pericardial chamber. In a 

 mussel 8 cm. long it has a length of 15 mm. and a breadth of 2 mm. when relaxed. 

 When distended with blood the diameter becomes about 4 mm. The blood leaves the 

 heart by a single aorta which leads off from it at the anterior extremity. The middle 

 of the ventricle is traversed by the rectum which enters at the anterior end just above 

 the aorta and passes out at the posterior extremity in the dorsal region, so that a blind 

 sac is left in the posterior end of the ventricle. 



The auricles are two large sacs which are symmetrically placed one on each side 

 of the ventricle and connected with it by a short auriculo-ventricular canal (fig. 131, 



