96 PHYLUM MOLLUSCA 



cavity. Put the blowpipe through the respiratory pore and blow 

 into the mantle cavity. It will be seen to extend from the collar 

 to the posterior side of the first whorl. Examine the mantle wall 

 with a hand lens and against the light. The network of blood 

 vessels which constitutes the lung will be seen. On the hinder 

 border of the mantle cavity note the kidney, an elongated, light- 

 colored, triangular organ ; just in front of it and beneath it — that 

 is, between it and the mantle cavity — is the heart within the peri- 

 cardium ; note the two chambers of the heart, the dorsal auricle 

 and the more ventrally placed and larger ventricle. Back of the 

 kidney is the dark-colored liver, which, with the intestine and 

 the light-colored reproductive tract, occupies the remainder of the 

 coils of the spiral. Note the rectum, a broad tube on the inner 

 (right) border of the mantle cavity going to the anus. Cut a small 

 hole in it, and through this pass a probe to the anus. 



The Mantle Cavity. Lay this open in the following way : with 

 fine scissors cut through the collar at the respiratory pore ; then 

 make an incision in the mantle wall from this opening, following 

 the collar round the outer side of the whorl to the heart ; con- 

 tinue the incision across the artery leading out of the heart, and 

 through the delicate membrane between the liver and the kidney 

 to the rectum, at the inner border of the whorl. The mantle can 

 now be laid back and its cavity with the organs exposed. The 

 broad rectum will be seen running along the entire inner border of 

 the mantle cavity. Now make an additional incision from the 

 respiratory pore along the inner (lower) border of the rectum as 

 far as the kidney. Lay back the mantle and pin it down as flat as 

 possible under water. Identify the heart within the pericardium, 

 the kidney, and the rectum. 



The Respiratory and Circulatory Systems. Observe the lung 

 (the network of blood vessels in the inner surface of the mantle) 

 and the large pulmonary vein, which runs along the kidney to the 

 heart. Slit open the pericardium. The two chambers of the heart 

 will be more distinctly seen, the thin -walled auricle into which the 

 vein runs and the larger ventricle. Back of the latter the aorta 

 passes into the viscera ; its cut end will be seen. 



The process of respiration and circulation is the following: 



