WORMS 



45 



front portion of this tube arise several large tubular rings 

 or "hearts" which are contractile and serve to keep the 

 blood circulating. They lead to a ventral vessel below the 

 food tube (Fig. 74). The blood is red, but the coloring 

 matter is in the liquid, not in the blood cells. 



Nervous System. — Between the ventral blood vessels 

 is a nerve cord composed of two strands (see Fig. 75). 

 There is a slight swelling, or ganglion, on each strand, in 

 each segment (Fig. 75). The strands sepa- 

 rate near the front end of the worm, and a 

 branch goes up each side of the gullet and 

 enters the two pear-shaped cerebral ganglia, 

 or "brain " (Fig. 75). 



Food. — The earthworm eats earth contain- 

 ing organic matter, the inorganic part passing 

 through the vent in the form of circular casts 

 found in the morning at the top of the earth- 

 worm's hole. What else does it eat ? 



The earth worm needs no teeth, as it 

 excretes through the mouth an alkaline fluid 

 which softens and partly digests the food 

 before it is eaten. When this fluid is poured out upon a 

 green leaf, the leaf at once turns brown. The starch in 

 the leaf is also acted upon. The snout aids in pushing 

 the food into the mouth. 



Kidneys. — Since oxidation is occurring in its tissues, 

 and impurities are forming, there must be some way of 

 removing impurities from the tissues. The earthworm 

 does not possess one-pair organs like the kidneys of 

 higher animals to serve this purpose, but it has numerous 

 pairs of small tubular organs called nephridia which serve 

 the purpose. Each one is simply a tube with several coils 

 (Fig. 76). There is a pair on the floor of each segment 



Fig. 75. — 



Ganglia 

 near Mouth 



and part of 

 nerve chain of 



earthworm. 



