8. Where are the appendages attached? Study a walking leg and describe its general construction, the number and kind of joints, the direction of motion in each joint, and the range of motion for the whole leg. Study an antenna in the same way. What methods are used in the crayfish to secure a wide range of motion? To secure flexibility? 9. Carefully split a crayfish into right and left halves. To do this, first cut through the ventral exoskeleton from end to end with scissors, then with a sharp knife or razor cut through to the dorsal exoskeleton and cut that with the scissors. Study one half, to get a better idea of the attachment of the appendages. These may then be removed and placed in order on a piece of paper upon which a list of the appendages has been written. 10. How many pairs of appendages are there? How may they be grouped according to location; how grouped according to function? How many pairs are there in each group? 11. What similarities of structure do you find in nearly all of the appendages? Assuming a swimmeret of the third, fourth, or fifth somite to be the least changed from the primitive type, what changes were necessary to make the sixth swimmeret; the third maxilliped; the walking legs; the antennæ; the antennules? 12. Remove the part of the carapace which covers a gill chamber. What are the boundaries of the chamber? Where does it open to the water? 13. Describe the appearance and the texture of a gill. How are the gills kept moist when the crayfish is in water; when it is on land? Why should they be kept moist? 14. Would you class the gills as external structures or as internal? Why do you think so? To what are they attached? How are the gills affected by the motion of the legs? 15. What work goes on in the gills? How is the supply of oxygen renewed? In this connection, try a live crayfish, kept quiet in water just about deep enough to cover it. Float bits of paper near it or carefully place a drop of ink in the water near it. By some such method currents of water may usually be shown, and their direction determined. Consider also the habitual motions of mouth parts and swimmerets, the bubbles sometimes seen when a crayfish is dropped into water and the habit crayfishes have of lying on one side, close to the surface of the water. Summary of the Study of Crayfishes To summarize your study, write a connected account of the relations of crayfishes to their environments, under the following topics:-- 1. What are the varying conditions in their surroundings which crayfishes must meet? Which are most important? 2. What conditions must be maintained in order that crayfishes may succeed, _i.e._ may live and reproduce? 3. How does a crayfish know what are the conditions around it? 4. How is it fitted to meet these conditions? (Answer in the following details):--