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HOW DO WE CLASSIFY ANIMALS? 



anterior end ; the setae there are anchored, then a wave of muscular 

 contraction passes down the body, shortening the body by drawing 

 up the posterior end. 



How the earthworm digs holes. The earthworm is not provided 

 with hard jaws or teeth. Behind the mouth opening is a part of 

 the food tube called the pharynx. It acts as a suction pump and 



draws particles of the soil into 

 the food tube. Organic matter 

 in the soil is used as food and 

 the unused soil is passed out 

 of the body and deposited on 

 the surface of the ground, in 

 the form of little piles called 

 worm casts. Charles Darwin 

 calculated that fifty-three 

 thousand worms may be found 

 in an acre of ground and that 

 ten to fourteen tons of soil 

 might pass through their bodies 

 in a single year. 



Life processes of the earth- 

 worm. The digestive tract of 

 the earthworm is an almost 

 straight tube inside of another 

 tube. The latter is divided 

 by partitions which mark the 

 boundary of each segment. 

 The outer cavity is known as 

 the body cavity, and the inner 

 cavity as the digestive tube. 

 Food is digested within the 

 food tube, passed through the walls of this tube by means of 

 osmosis, and is absorbed by the blood which carries it to various 

 parts of the body. The earthworm has no gills or lungs. The 

 moist skin acts as an organ of respiration, taking in oxygen and 

 giving off carbon dioxide. The nervous system is on the ventral 

 side of the body but forms a ring around the food tube in the 



— — upper lip 



brain 



—-pharynx 

 — nerve cord 



Tieart 



-testis* 



14 ovary 



crop 



T — &5yxr* 



-cforsal artery 

 - intestine, 



A longitudinal section through an earthworm. 

 In what segments are the hearts, the crop, the 

 gizzard, the brain, the reproductive organs ? 



