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Segmented Worms — The Annelids 



If you like to go fishing you surely have some acquaintance with at 

 least one member of this phylum. The earthworm, which is the most 

 abundant genus in this group, is noted for its ability to entice fish to bite, 

 and no picture of a young American going out to fish would be complete 

 without a pole and a can of worms. However, serving as fish bait is 

 not, by any means, the greatest economic importance of the earthworm as 

 we shall soon learn. Worms in this phylum are characterized by seg- 

 mented bodies. The phylum name means little ring, and as you look at 

 one of these worms you will see that the segments resemble a series of 

 little rings joined together to make the entire animal. 



Because of its abundance, economic importance, and the typical arrange- 

 ment of organs, we will choose the earthworm, Lumbricus terrestris, as a 

 type animal for the phylum. Earthworms may be found almost every- 

 where that there is moist soil, and their tremendous value to agriculture 

 can hardly be overestimated. They have a habit of eating the dirt as 

 they crawl through it when it is closely packed and it passes through 

 their bodies to be left behind. This makes the soil loose and porous so 

 that plant roots can easily penetrate it and at the same time makes it 

 spongy so that it will hold the rain that falls. Also, the wastes from the 

 earthworms' bodies add to the fertility of the soil, and it is doubtful if 

 the farmer could find a better friend than the earthworm. 



Life Processes of the Earthworm 



The life processes of the earthworm show many interesting develop- 

 ments and, since many of these are similar to those of higher animals, 

 we shall survey them in some detail. 



Respiration is carried on by direct absorption of oxygen through 

 the skin, and carbon dioxide is given off from the same area. The 

 skin must be continually moist or this exchange cannot take place and 

 the worms will suffocate. The earthworms move up or down in the soil 

 according to the region where the conditions of moisture are best suited 

 to their needs. They go deep in dry weather and come up when the 

 soil becomes saturated at the lower levels. They may even leave their 



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