How To Study Living Animals


Directions.

In a section under a simple lens, identify the dorsal and ventral surfaces, the body wall, the body cavity, the alimentary canal, and, if possible, the dorsal and ventral blood vessels and the ventral nerve cord herunterladen.

Under a microscope identify the same structures. Notice that the body wall consists of three layers of cells: an outer single layer, the epidermis; a middle layer, the circular muscles; and an inner one, the longitudinal muscles herunterladen.

The nephridia show as loosely scattered fragments in the body cavity, at the right and left of the alimentary canal.

If you happen to have a section which shows one or more setæ, identify the muscles which operate it, and the group of glandular cells at its inner end, which are known as setigerous (from seta) cells microsoft office kostenlos downloaden vollversion deutsch chip.

Questions.

1. Describe the epidermal cells. What is their probable function? Among them notice larger cells, clear and rounded. These are themucous (slime) cells.

What is the use of mucus to the worm?

2. Describe the muscle cells. In which direction do the muscle fibers extend? What is their function? Which layer of muscle cells is thicker, the circular or the longitudinal? Why should it be?

3. Notice the cells in the walls of the alimentary canal. What layers do you find? How are they arranged?

4. If the section you are studying is a cross section from the region back of the gizzard, the alimentary canal will look horseshoe shaped, indented from the dorsal surface. What is the effect of this indentation upon the amount of surface in the alimentary canal?

5. Study the cells of the nerve cord. How do they compare in size and shape with the muscle cells?

Suggested drawings.

a. A diagram of a cross section, showing the relation of the organs.

b. A diagram of a longitudinal section, at least through the body wall, to show the arrangement of muscle fibers.

c. A drawing of a portion of the body wall, to show details.