How To Study Living Animals


The External Structure of the Fish
Materials.

Freshly killed or preserved fish in dishes or shallow pans with enough water to prevent drying herunterladen. Simple or compound microscopes, forceps, and a bristle.

Directions.

Examine the fins and identify the membrane and the supporting rods, or rays, of bone or cartilage herunterladen. Notice how the ends of the cartilaginous rays keep the membrane from tearing.

Investigate the scales as to their arrangement, number, and size microsoft office kostenlos downloaden vollversion deutsch chip. Remove a small patch of scales along the lateral line to find how they are attached, where the fish’s color is situated, and how access to the sensory organs of the line is permitted. Examine a scale under the microscope.

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.