VASCULAR SYSTEM OF THE EARTHWORM 141 



is mixed with the worm's food the colored granules reappear 

 in the absorptive cells; chlorophyll and fat have also been 

 detected. t 



The Rectum. The rectum of the earthworm is the posterior 

 part of the intestine which bears no typhlosole. It opens to the 

 outside through the anus which is provided with a sphincter 

 muscle. According to Hensen, each worm deposits 1/2 gram 

 of faeces in 24 hours and these faeces make up the castings shown 

 by Darwin to have great economic importance. 



Further Fate of the A bsorbed Nutriment. The gut walls of the 

 earthworm are richly supplied with blood vessels* and finer 

 capillaries which form a vascular network throughout the entire 

 intestine. It is highly probable, although never demonstrated, 

 that the absorbed food material is passed directly into tjie blood 

 through the walls of these vessels. 



E. BLOOD VASCULAR SYSTEM. In the earthworm it is the 

 plasm or fluid that is colored refUby haemoglobin while the 

 living cells of the circulation are colorless. As>in vertebrates, 

 the blood flow is continuous, the circulation being closed 

 throughout. The main trunks are (i) a dorsal vessel lying on 

 the digestive tract and giving off in the anterior segments five 

 pairs of enlarged vessels, the so-called " aortic arches" or loops. 

 These loops are connected below the oesophagus with (2) a 

 ventral vessel also running the entire length of the animal 

 below the digestive tract. Both dorsal and ventral vessels 

 give off branches to the adjacent tissues. One pair leaves 

 the dorsal vessel in each somite and runs along the dissepiment 

 to the body wall where it splits into numerous fine branches 

 penetrating the dermal musculature and the epithelium. Other 

 branches of the dorsal vessel are given off to the digestive tract 

 ending in capillaries in the walls of the stomach-intestine and 

 other organs. In the anterior region two lateral vessels are 

 given off which supply the reproductive organs. Three other 

 longitudinal ventral vessels run the length of the worm; one, 

 the sub-neural vessel, lies below the nerve cord while two 

 others, supra-neurals, are embedded in the connective tissue 

 about the nerve cord, one on each side (Figs. 55 and 57). 



