242 GENERAL ZOOLOGY 



forward, take up the waves of contraction sent along the 

 dorsal vessel, and force the blood into the ventral blood ves- 

 sel, which carries it posteriorly in a regular flow. Below the 

 ventral nerve chain is the subneural blood vessel, in which the 

 blood probably flows backward. The lateral blood vessel, with 

 its connections, is limited to the region anterior to the crop. 

 Capillaries (fine blood vessels joining larger ones) branch 

 in the wall of the intestine and connect in a very complicated 

 fashion with all the large vessels. Absorbed food passes into 

 the capillaries and is carried with the blood to the larger 

 blood vessels, to be transported to all parts of the body. 

 All about the intestine, in the hollow spaces of the somites, 

 there is a large quantity of body-cavity fluid, which is very 

 much like the blood in the vessels, except that it is colorless. 

 It is thought that much of the absorbed food mixes with 

 this fluid. The outcome is the same with food carried by 

 the regular circulatory system and with that taken up by 

 the body-cavity fluid. This food is carried by the blood and 

 body-cavity fluid to all parts of the body, where it is assim- 

 ilated by the tissues. 



Respiration. The earthworm has neither gills, tracheae, 

 nor lungs; still it can breathe quite as perfectly as the 

 animals which possess one or another of those organs. The 

 outer skin of the earthworm is thin and moist, and just 

 beneath it are capillaries. While in its burrow, or even in 

 water, air comes in contact with the skin, and its most im- 

 portant element, oxygen, passes through and mixes with 

 the blood. At the same time the blood in the capillaries 

 gives up its carbon dioxide, which passes through the skin 

 into the air. 



Excretion. Carbon dioxide is given off only from the skin ; 

 water probably in part from the skin ; uric acid and water 

 are discharged from pairs of small funnel-shaped tubes in 

 the lateral portions of the cavity of the somites. These 



