392 Animal Biology 



results in a mutual exchange of sperms but no discharge of eggs or fer- 

 tilization at this time. One earthworm cannot fertilize its own eggs, but 

 there is a mutual, cross-fertilization in the cocoon. 



After copulation, the worms pull away from each other and half of 

 the slimy band is slipped over the anterior end of each worm. In doing 

 so, the eggs from the oviducts are discharged into the slimy tubes which 

 also receive sperms from the seminal receptacles (segments IX and X). 

 The elastic ends of the cocoons close to imprison sperm, eggs, and a 

 liquid food for the developing embryos. A young worm eventually 

 breaks from the cocoon and shifts for itself in the soil. After a few 

 weeks the embryo becomes an adult. 



QUESTIONS AND TOPICS 



1. List the distinguishing characteristics of the phylum Annelida. 



2. In what ways is the earthworm to be considered a higher type of animal than 

 those studied previously? Be specific in your answer. 



3. Explain and give the significance of ( 1 ) metamerism, (2) coelom, (3) "closed 

 type" of circulatory system, (4) typhlosole, (5) hemoglobin, (6) lymph, 

 (7) setae with their muscles, (8) calciferous glands, (9) triploblastic, and 

 (10) clitellum. 



4. Explain why earthworms appear to be "rained out" after a rain. 



5. Discuss the economic importance of earthworms. 



6. Explain the advantage of having both male and female sex organs in the same 

 earthworm, especially when the method of copulation is taken into considera- 

 tion. 



7. In what specific ways are the nervous system and sensory equipment more 

 highly developed than in animals studied previously? What is the significance 

 of this? 



8. Describe each of the following in the earthworm: (1) integument, (2) 

 motion and locomotion, (3) ingestion and digestion, (4) circulation, (5) 

 respiration, (6) excretion and egestion, (7) coordination and sensory equip- 

 ment, and (8) reproduction. 



9. Why do you think an earthworm needs so many pairs of nephridia? Explain. 

 10. List the conclusions you can draw from your studies of the earthworm. 



SELECTED REFERENCES 



Beddard: Earthworms and Their Allies, Cambridge University Press. 



Buchsbaum: Animals Without Backbones, University of Chicago Press. 



Darwin: The Formation of Vegetable Mould Through the Action of Worms, 



London, John Murray Co. 

 Hegner: Invertebrate Zoology, The Macmillan Co. 



