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the mantle there is a network of thin-walled blood-vessels ; 

 in these the blood is aerated. 



The venous blood from the body is collected into the 

 pulmonary sinus which passes round the mantle-cavity 

 where the mantle joins the body - wall. Afferent veins 

 from this sinus are connected (by the network of thin- 

 walled vessels in which the blood is purified) to efferent 

 vessels ; and these pass into the pulmonary vein which 

 receives a vessel from the kidney and enters the auricle 

 of the heart. The pure or arterial blood is pumped by 

 the ventricle into two main arteries which give off branches 

 to the various organs and tissues. 



The two-chambered heart (auricle and ventricle) is 

 enclosed in a sac, the pericardium, situated at the back of 

 the mantle on the left side. 



Describe the Excretory System of Helix. 



Beside the pericardium there is a greyish and somewhat 

 triangular kidney ; its duct, the ureter, passes along the 

 dorsal side of the rectum and opens to the outside above 

 the anus. There is a narrow ciliated passage, the reno- 

 pericardial canal (nephrostome), between the kidney and 

 the pericardium. 



Write an Account of the Reproductive Organs of the Snail. 



Near the top of the spire and embedded in the "liver," 

 there is a small yellowish hermaphrodite gland or ovotestis 

 in which ova and sperms are formed, but at different times. 

 The white and sinuous hermaphrodite duct leads to the base 

 of the tongue-shaped albumen gland, from which a nourish- 

 ing fluid is received. Where the duct enters the gland, 

 a common duct arises ; it passes forward to near the head ; 

 it is wide and consists of two parallel but distinct passages, 

 the one, along which the ova pass, being more convoluted 

 than the other, along which the sperms travel. The two 

 passages diverge as separate male and female ducts. The 

 female duct or oviduct is short and thick, and it leads 

 into a muscular tube, the vagina, into which the following 



