184 
THE WORM GROUP 
170. Other Annelids. — The sand worm or Nereis (ne'- 
re-is), a marine or salt-water form, is another segmented 
annelid. It is more highly specialized than the earthworm, 
for it has biting mouth parts, tentacles, and eyes. It is an 
active swimmer at times. The development of the sand 
worm exhibits metamorphosis, while the earthworm hatches 
directly into a worm without metamorphosis. 
SUMMARY 
In the worm group are included the unsegmented worms, 
such as tapeworms, liver flukes, and hair worms; and the 
segmented or true worms such as the earthworms, sea-worms, 
and leeches. All these worms have more perfectly or¬ 
ganized parts than the sponges and hydroids. The body of 
the earthworm shows the first steps in the formation of 
definite front, back, and ventral regions. The digestive 
tube is also specialized into pharynx, esophagus, crop, 
gizzard, and stomach-intestine; and the name brain may 
be given to a slightly enlarged portion of the anterior end 
of the nerve cord. Small worms of various kinds are numer¬ 
ous in stagnant water. Some live as parasites in man and 
other animals, causing much suffering and loss of life. The 
earthworm as a cultivator of the soil has been of inestimable 
value to man. 
QUESTIONS 
What kinds of animals are called worms? Is it proper to call “ cur¬ 
rant worms” worms? Why not? What are they? How do you 
recognize the anterior, posterior, dorsal, and ventral regions? Compare 
the grasshopper or some other insect with the worm. Explain how the 
earthworm moves; makes its burrow. Compare the digestive tube 
with the digestive sac of the hydra. 
REFERENCES 
Darwin, Earthworms and Vegetable Mould. 
Jordan, Kellogg, and Heath, Animal Studies, Chapter VI. 
Sedgwick and Wilson, General Biology. 
