A SQUID 109 



these they are much wider, but are very thin-walled and not easily 

 seen. Trace them as far as possible. Observe again the mantle 

 veins, which bring blood from the mantle to the branchial hearts. 

 The course of the blood is the following : it enters the branchial 

 hearts through the postcaval, precaval, and mantle veins ; the 

 contraction of these hearts sends it into the branchial arteries 

 which pass along the upper side of the gills ; it then traverses the 

 delicate, transverse filaments of the gills and becomes oxygenated, 

 when it collects again in the branchial veins on the opposite side 

 of the gills ; through these it passes to the systemic heart, whence 

 it is sent through the anterior and posterior aortas to the different 

 parts of the body. 



Exercise 3. Make a diagrammatic drawing of the circulatory and the 

 respiratory systems. 



The Digestive System. Remove the kidneys and precaval veins. 

 Beneath them will be seen a large, glandular, bilobed organ of some- 

 what doubtful function, called the pancreas. At its forward end a 

 pair of cylindrical organs, the liver ducts, will be seen entering it 

 from the liver. The pancreas is made up of anastomosing, glan- 

 dular projections of the walls of these ducts. Remove the gills, 

 branchial hearts, systemic heart, and hinder arteries. The deH- 

 cate body wall should be completely removed from the entire vis- 

 ceral mass, and great care be taken not to injure the stomach 

 pouch beneath. This latter organ is a large bag with thin, trans- 

 parent walls which extends to the extreme hinder end of the body ; 

 beneath it will be seen the large testis or ovary, according to the 

 sex of the animal. This pouch is not really a part of the stomach, 

 notwithstanding its name, but is a reservoir for the secretions of 

 the liver, which communicates with it through the liver ducts. 

 Carefully loosen the stomach pouch without separating it from 

 the body and let it float in the water of the dissecting pan. It 

 communicates with the thick-walled stomach, which hes just in 

 front of it, but food substances are prevented from passing into it 

 from the stomach by valves. Loosen the stomach, noticing that 

 it is bound to the ovary or testis by an artery, the genital artery. 

 At the forward end of the stomach are the intestine and the oesoph- 



