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 colouring 

 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; 

 these are found in the morning at the top of 

 the earthworm's burrow. 



The earthworm has no teeth. 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 imparities 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. 

 There is a pair on the floor of each segment. Each neph- 



Fig. 75.— 



Ganglia 

 near Mouth 



and part of 

 nerve chain of 



earthworm. 



