A. Methods of Reproduction

1. The Simple or Asexual Method of Reproduction
Materials.

Slides or diagrams, showing a dividing amœba, a dividing paramecium, a dividing vorticella, reproduction in some form of sporozoa, budding hydra, gemmules of spongilla, and some species of worm as Dero or Nereis in the process of dividing.

Definitions.

Spore, a cell capable of developing into a new organism. Asexual reproduction, reproduction by division of the cell or body. Sexual reproduction, reproduction by means of the conjugation of two reproductive cells known as the egg and sperm cells. Fertilization, the fusion of the male or sperm cell with the egg or female cell. Ovary, an organ producing eggs. Spermary, an organ producing sperm cells. Cross fertilization, fertilization in which the sperm and egg cells are produced by different individuals. Diœcious, the different kinds of reproductive organs found in different individuals. Monœcious, the different kinds of reproductive organs found in the same individual.

Directions.

Note.—Refer to your notes, if the animals mentioned in these exercises have been already studied. This exercise may be largely review.

Study the methods of reproduction in the specimens or diagrams before you. Determine first, in what respects the methods of reproduction are similar in all; second, in what respects there is a variation.

Questions.
  1. What has an amœba gained by dividing? What powers has each new cell that the original amœba had lost? What would have been the fate of the amœba if it had not divided into new cells?
  2. What various forms of cell division did you find?
  3. What is the simplest method of reproduction?
2. The Complex or Sexual Method of Reproduction
Materials.

Slides or diagrams showing hydra and sponge reproducing sexually. Conjugating paramecia, fertilized and unfertilized starfish eggs.

Directions.

Identify the reproductive organs or gonads of the hydra. These are slight swellings on the surface. The one nearer to the mouth end is the spermary and that near the attached end is the ovary.

Questions.
  1. How is an egg cell produced in hydra? In general how do the reproductive cells of sponges and hydra originate?
  2. What is gained by limiting the process of reproduction to special cells?
  3. What is the difference between the appearance of the nucleus of the fertilized and the unfertilized egg?
  4. What is the advantage of cross fertilization? How accomplished in Hydra? What reason can you suggest for the spermary's position?
  5. Describe the conjugation of a paramecium.
  6. Describe the process of maturation and fertilization in a starfish egg.
Suggested drawings.
  1. Diving Amœba or Paramecium.
  2. Budding Hydra.
  3. Hydra showing gonads.
  4. Starfish egg—fertilized and unfertilized.

Summary of important points in the study of methods of reproduction:—

  1. What are the two principal methods of reproduction? How do they differ?
  2. Why is reproduction necessary?