[Illustration: FIG. 85.--1, mandible; 2, 3, maxillæ; 4, 5, 6, maxillipeds.] =Legs.=--How many legs has the crawfish? How many are provided with large claws? Small claws? Is the outer claw hinged in each of the large grasping pincers? The inner claw? [Illustration: FIG. 86.--CRAWFISH (ventral surface).] =Appendages for Taking Food.=--If possible to watch a living crawfish eating, notice whether it places the food directly into the mouth with the large claws. Bend the large claws under and see if they will reach the mouth. Attached just in front of the legs the crawfish has three pairs of finger-like appendages, called foot jaws (maxillipeds), with which it passes the food from the large pincers to its mouth (Figs. 85, 86). They are in form and use more like fingers than feet. In front of the foot jaws are two pairs of thin jaws (maxillæ) and in front of the thin jaws are a pair of stout jaws (mandibles) (Fig. 85). Do the jaws move sidewise or up and down? Which of the jaws has a jointed finger (palp) attached to it? Do all of the appendages for taking food have both exopod and endopod branches on a basal stalk or protopod? Which of the appendages have a scalloped edge? How would you know from looking at the crawfish that it is not merely a scavenger? Why are there no pincers on the hind feet? [Illustration: FIG. 87.--Gill cover removed and gills exposed. _Mp_, gill bailer.] =Sense Organs.=--Find the _antennæ_, or long feelers (Figs. 82, 90). Are the antennæ attached above or below the eyes? (Fig. 87.) [Illustration: FIG. 88.--LENGTHWISE SECTION OF MALE CRAWFISH. _c_, heart; _Ac_, artery to head; _Aa_, artery to abdomen; _Km_, stomach; _D_, intestine; _L_, liver; _T_, spermary; _Go_, opening of sperm duct; _G_, brain; _N_, nerve chain.] Find the pair of _antennules_, or small feelers. Are their divisions like or unlike each other? Compare the length of the antennules and the antennæ. Compare the flexibility of the antennæ with that of the other appendages. Observe the position of the _eyes_ (Figs. 81, 88). How long are the eyestalks? Is the stalk flexible or stiff? Touch the eye. Where is the joint which enables the stalk to move? Is the outer covering of the eye hard or soft? A mounted preparation of the transparent covering (cornea) of the eye, seen with lower power of microscope, reveals that the cornea is made up of many divisions, called facets. Each facet is the front of a very small eye, hundreds of which make up the whole eye, which is therefore called a compound eye. The elongated openings to the _ear sacs_ are located each on the upper side of the base of a small feeler just below the eye.