72 Invertebrate Zoology. 



will be seen. Anteriorly, each organ opens through a small 

 pore that thus leads from the nephridium to the mantle 

 cavity. Each pore lies near the median line, some little 

 distance in front of the branchial heart, and marks the 

 anterior end of the nephridial chamber. The posterior and 

 broader end of the chamber lies just medially of the branchial 

 heart, the right and left nearly meeting in the median line. 



Two arteries, lateral mantle arteries, will be noticed (one 

 on each side), extending laterally and posteriorly, from near 

 the point where the median mantle artery leaves the visceral 

 mass, to the internal surface of the mantle. Lying laterally 

 to each lateral mantle artery is a much larger thin-walled 

 posterior vena cava. This organ is often filled with blood 

 that has been received from the posterior mantle veins which 

 lie parallel to the mantle artery. The cone-shaped posterior 

 portion of the mantle cavity is filled up with the voluminous 

 visceral sac and the sexual organs. 



Make an outline drawing of the organs as they naturally 

 lie in the mantle cavity. 



The Circulatory System. By the use of a hypodermic 

 syringe the circulatory system may be injected and the fol- 

 lowing points determined. 



Each post-cava empties its blood into the branchial heart of 

 the same side, which also receives the blood that has been re- 

 turned from the anterior portion of the animal through the/;r- 

 cavce. The latter traverse the glandular walls of the nephridial 

 chambers. Each branchial heart also receives an anterior 

 mantle vein, returning blood from the anterior portion of the 

 mantle. Impure blood is forced from the branchial heart 

 to the gills along the afferent branchial vessel which traverses 

 the edge of the gill that is directed towards the mantle. 



