SEA MUSSEL MYTILUS EDULIS. 



155 



biuret test, while the xanthoproteic acid is not pronounced. Glycogen is present in 

 small quantities. 



The volume of blood present in an animal varies with its size and condition. By 

 cutting the posterior adductor muscle, after thoroughly draining a shellfish of the sea 

 water held within the mantle cavity, it is possible by gently pressing the fleshy parts to 

 extract most of the hasmolymph. The quantity obtained from well-nourished mussels 

 about 3 inches long is between 5 and 6 cc. 



PHYSIOLOGY. 



The function of the circulatory system is to carry dissolved food materials and 

 oxygen to the various tissues of the body and to remove the carbon dioxide and other 

 waste products of metabolism. This is accomplished by the circulation of blood, or 

 haemolymph, through the system of arteries and veins which have been described. Cir- 

 culation is maintained by regular pulsations of the heart, which in the adult beats at 

 the rate of 25 to 30 times per minute when the body temperature is 20 C. 



136 



137 



Fig. 136. — Blood corpuscles drawn from life. X560. a, contracted condition; ft.showmg pseudopodia formed during loco- 

 motion; c, tangled group of obrpuscles. 



Fig. 137. — Blood corpuscles drawn from histological section. X560. Fixed in f'.ilson fluid and stained with Heidenhain 

 iron hematoxylin. 



The character of the heart beat is somewhat similar to that of the vertebrate. At 

 first the auricles contract. This is followed immediately by a slight dilation of the 

 posterior end of the ventricle, and then a wave of contraction moves forward rapidly 

 over it. At the same time the ventricle contracts and discharges its blood into the 

 aorta the auricles dilate with blood received from the oblique vein. This is followed 

 by a period of rest, and then the process repeats itself. 



The blood forced into the ventricle by contraction of the auricles is prevented 

 from returning by the presence of auriculo-ventricular valves. In like manner blood 

 pumped from the ventricle into the aorta is prevented from flowing back by valves 

 present in both the anterior end of the ventricle and in the aortic bulb. 



The blood flows from the aorta to the different organs of the body through a system 

 of arteries which ultimately break up into a lacunar network of vessels that pervade all 

 the tissues. The main arterial vessels lie on the outer surfaces of the mantle and run 

 through the deeper parts of the body where the carbon dioxide accumulates in greatest 



