242 



HITCHCOCK'S ANATOMY 



431. Circulation in Molluscs. — The higher orders of 

 molluscs show a system of circulating vessels which seem to 

 be arteries and veins, with a central vessel answering to a 

 heart. There is usually a ventricle corresponding to the 

 right ventricle in man, to send the blood to the respiratory 

 organ. There is also another cavity which corresponds some- 



FlG. 245. 



Anatomy of the Snail, cr, Mouth, b, Foot. <?, Lung. 0, Stomach. / Intestine, 

 Liver. /1, Heart, i, Aorta, j, Gastric Artery. I, Hepatic Artery, k, Artery of the 

 Foot, m, Abdominal Cavity. Canal conveying the Blood to the Lungs. 0, Vessel 

 carrying Blood from Lung to Heart. 



what to an auricle, which receives the blood as it enters the 

 heart. But w r ith the exception of the vessels carrying blood 

 to the gills, there are few separate tubes for carrying this 

 fluid through the body, it being left to circulate by imbi- 

 bition, or it is effected by means of the lacunar spaces, Fig. 

 245. 



432. Blood of Molluscs. — The blood of these animals is 

 generally destitute of corpuscles, and is sometimes colorless, 

 though often white, brown, red, or green. 



433. Contractions of the Heart, — The heart does not 



431. What are the circulatory vessels in molluscs? How is most of the fluid circu- 

 lated ? 432. What of the blood of molluscs ? 



