WORMS 



211 



blood passes slowly forward. The whole dorsal blood vessel, and 

 especially several tubes which connect it with a ventral vessel on 

 the opposite side, are contractile. These connecting tubes are 

 known as hearts, because they serve to pump the blood in a 

 definite direction. Compare the rate of pulsation with your own 

 pulse. 



Respiration. — No gills or lungs are present, the thin skin acting 

 as an organ of respiration. But the worm is unable to take in 

 oxygen unless the membranelike skin is kept moist. Respiration 

 in the earthworm is simply the exchange or osmosis of gases 

 through the skin, the oxygen passing into the blood, the carbon 

 dioxide formed from the oxidation taking place within 

 the body of the worm passing out. 



Development. — Notice in some worms the swollen area 

 (about one third the distance from the anterior end) called the 

 girdle or clitellum. This area forms a little sac in which the 

 eggs of the worm are laid. As it passes toward the anterior 

 end of the worm, it receives the sperms and a nutritive fluid 

 in which the eggs live. The fertilized eggs are then left to 

 hatch. The capsules may be found in manure heaps, or under 

 stones in May or June ; they are small yellowish or brown bags 

 about the diameter of a worm. If possible, procure some 

 young worms and compare them with older ones. 



Regeneration. — Earthworms possess to a large degree 

 the power of replacing parts lost through accident or other 

 means. The anterior end may form a new posterior end, 

 while the posterior end must be cut anterior to the clitellum 

 to form a new anterior end. This seems to be in part due to 

 the greater complexity of the organs in the anterior end. 



The Sandworm. — Other segmented worms are familiar 

 to some of us. The sandworm, used for bait along our 

 eastern coast, is a segmented worm which lives between tide 

 marks in sandy localities. It is plainly segmented, each seg- 

 ment bearing a pair of locomotor organs called parapodia 

 (meaning side feet). A part of each parapodium is prolonged 

 into a triangular gill. The animal has a distinct head, which 

 is pro^dded with tentacles, palps, and eye spots. The mouth has a pair r! 

 hard jaws which may be protruded. In this way the animal seizes and 

 draws prey into its mouth. The sandworm swims near the surface of the 

 water, the body bending in graceful undulations as the parapodia. like little 

 oars, force the worm forward. They spend most of the time in tubes in 



A marine worir 

 {Nerds). 



