a. How wide a food range has it, _i.e._ how many kinds of food does it eat? How does it find its food? How does it reach it? How does it take its food? How does it make food small enough to be eaten? b. What are the organs for taking in oxygen? Where are they? How are they attached? How is the supply of oxygen kept up? How are the organs kept from drying, from clogging, and from mechanical injury? c. What ranges of temperature can crayfishes endure? What temperature is best? How do they avoid fatal extremes? d. What are the enemies of crayfishes? What protection against these have they? e. How often do crayfishes reproduce? About how many times during a normal lifetime? About how many eggs are there and how many of them hatch? What care is given to the eggs and to the young? About how many of the young reach maturity? (_Suggestion._ Do the crayfishes of a region vary noticeably in numbers from year to year?) 5. What limits the range of crayfishes, north and south? What limits it on land? What in water? 6. When the crayfishes of a given locality are not well adapted to it, what can they do? _Suggested drawings._ a. The whole animal, dorsal surface, preferably without appendages. b. One of each pair of appendages, except where they duplicate. c. The tail-fin. Label the sixth swimmerets, the sixth and seventh somites. d. The gill chamber, with gills in position. Show circulation of water by arrows. e. A gill, to show construction. 2. COMPARATIVE STUDY OF CRUSTACEA _Materials._ Get together all the different specimens of crustacea you can collect, and identify the material. Then study each specimen as follows:-- _Questions._ 1. Briefly describe the exoskeleton, if there is one. 2. What region or regions are clearly segmented? 3. How much of the body is covered by a carapace? 4. Has it segmented appendages? Classify the appendages as to their use. 5. Are the cephalo-thorax and abdomen equally developed? If not, which is more developed? 6. How many antennæ has it? Are the eyes stalked, or are they sessile? 7. What organs of respiration has it? Where are they attached? 8. How many thoracic appendages has it, if any? 9. What methods of locomotion does it use? _Summary._ 1. Does this animal seem to be adapted to life on land or in water, or both? Give your reasons for your opinion. 2. What characteristics are common to all the crustacea you have studied? 3. REVIEW AND LIBRARY WORK ON CRUSTACEA 1. What are arthropods? 2. Give the classes of arthropods with an example of each. 3. What are the distinguishing characteristics of the class crustacea? 4. In what respects are most of the appendages of the crayfish homologous, _i.e._ alike in the plan of structure? Which do you consider the simplest, and why do you? Which do you consider the most specialized, and why?