Observe the eyes and identify the parts similar to those of the human eye: lid, lash, tear-duct, cornea, iris, and pupil. In front of and between the eyes, find the nostrils. By means of a bristle determine whether these are connected and whether they do or do not open into the mouth or the throat. _Questions._ 1. Make a list of the fins, classifying them according to their structure. 2. Bearing in mind the differences in structure and consequent action,--what can you say regarding the adaptation of the several fins for protection? for rigidity or flexibility in locomotion? 3. State how much of the body is covered with scales, and where the largest and the smallest ones are found. 4. How are the scales arranged with reference to each other? What benefit is derived from this in protection? in locomotion? If you have noticed any mucus or slime upon the body, state its use. 5. Do the scales or the skin bear the pigment? Give the color pattern of the kind of fish used in class. How would this be useful to the fish in its natural home? 6. Describe the structure of a scale and state how it is attached to the skin. In what way is the lateral-line scale specialized? 7. State how, when the fish is swimming, the nostrils catch odors. By means of a diagram, with arrows show the probable direction of the water current through the nose. 8. State which of the structures of your eye are present in the fish's eye, and which are missing. Could a fish weep? wink? How would a fish sleep? 9. Inasmuch as light penetrates water but a little way, so that objects can be distinguished only within about thirty feet, would the fish be nearsighted or farsighted? _Suggested drawings._ a. A side view of the entire fish, fully labeled. b. A bony rayed and a cartilaginous rayed fin. c. A scale, showing its minute structure. d. A dorsal or a lateral view of the head, showing the sense organs. The Mouth and the Gills of the Fish _Materials._ The same materials as those used in the preceding exercise may be used here. _Directions._ The mouth, its structure and its action, can be seen by pulling the upper jaw upward and forward until the mouth and the gill chambers open fully. Examine the structure and action of the jaws, the tongue, the throat, and the teeth on each jaw and on the roof of the mouth. Investigate the breathing apparatus from the throat side and from the exterior, noting the number, form, and structure of the gills, their attachment and their protection. The mouth may be kept open by a short splinter or a ball of paper. The pupil should identify the following structures:-- 1. _Gill_, an organ for breathing the air dissolved in water. 2. _Gill arch_, an arch of bone or cartilage supporting the gills. 3. _Gill filaments_, fringe-like structures attached to the gill arches, forming the gills. 4. _Gill raker_, lateral projections from the gill arches.