15. Trace the history of a tapeworm from the egg to the adult. At what stage are they most likely to be destroyed? What provision is there for this? What advantages are there to the host in the fact that a tapeworm's egg cannot develop in the original host? What advantages to the parasite? 16. What organs has a parasite lost, if it ever had them? How does it succeed without them? What connection is there between parasitism and degeneration? Can you decide which is cause and which is effect? If so, which is? 17. Why do worms so easily become parasitic? What advantages are there in becoming a parasite? What disadvantages? 18. What is radial symmetry? Name two animals which show it. What is bilateral symmetry? Name two animals which show it. What is the relation between locomotion and symmetry? 19. What is meant in biology by the term "regeneration?" To what extent have we this power? To what extent have hydra and earthworm? What are the results of this power? 20. Name various methods of locomotion among worms. Give examples. Name a fixed or sedentary worm. 21. What is the economic importance of worms? Consider here not only earthworms and tapeworms, but also the stomach worms of sheep, liver flukes, trichinæ, hookworms, vinegar eels, and as many others as you have time and books to look up. 5. THE CONNECTION BETWEEN STRUCTURE AND FUNCTION _A Review of the Work done on the First Four Groups of Animals_ Review all your studies on the protozoa, sponges, cœlenterates, and worms. Write the results in the following summary:-- 1. What work, _i.e._ labor, must an animal do to live? 2. How many cells are necessary to do this work? 3. When this work is divided among a number of cells, what is the effect upon the quantity and quality of work accomplished? 4. When this work is divided among a number of cells, how does the structure of the cells show it? How does the arrangement of the cells also show it? Give examples. 5. The technical expression for this specialization of cells, giving them different functions, is "division of labor." Formulate a clear definition for this expression, giving an example to illustrate it. 6. Is division of labor a good thing for an animal body, or is it not? Give reasons for your opinion, with examples for illustration. CHAPTER IV ADAPTATION TO SURROUNDINGS #A STUDY OF CRUSTACEA# #To Show the General Adaptation of an Invertebrate to its Surroundings# 1. A STUDY OF CRAYFISHES _Materials._ Crayfishes, living and preserved. Some of the living crayfishes should be established in conditions as natural as possible _i.e._ in an inch or so of fresh water, with rocks, weeds, etc., and left undisturbed. Small crayfishes are desirable to show locomotion in water. Living Crayfishes _Directions and observations._