A Guide for the Study of Animals Part 53

h.o.m.ology of the Vertebrate Skeleton

_Materials._

Prepared skeletons of an amphibian, a reptile, a bird, another mammal, and man. If any of these be lacking, lantern-slide ill.u.s.trations may be used in a partially darkened room.

_Observations._

Having studied the frog's skeleton in detail, the student can readily compare each of these types with it. Compare in a very general way the skulls, the girdles, and the limbs; their form and use. Note variations in the form and number of the vertebrae and the number of the ribs.

_Questions._

1. In which types of vertebrates are the joints between the skull bones bound with cartilage? How does the joining change in later types?

2. What dissimilarities occur in the series as regards closure or boxing in of the eye orbits, nostrils, and skull bones? How would these changes in joining and closure affect strength, rigidity, and protection?

3. What evidence is there that such improvement has affected brain capacity and intelligence?

4. State how the attachment of the skull to the vertebral column changes as the animal man a.s.sumes an erect position.

5. Are the vertebrae of these types alike in structure? What is the general form of an horizontally placed vertebra, as in the horse or a reptile, and of a vertically placed one, as in man? If you see any differences, account for them.

6. Wherever possible, find the vertebrae of the neck (cervical), and note the number of them in each case.

7. How is flexibility of the column accomplished in certain types or in certain places of one type? How is rigidity gained? State instances in each answer.

8. Examining the interior of the turtle's "sh.e.l.l," find out and explain how the vertebrae have been modified to form the upper "sh.e.l.l." How has the under portion (_plastron_) been formed?

9. In round numbers, which skeleton has the greatest number of vertebrae and which the least?

10. Which skeleton has the greatest number of ribs, and which has the least?

11. In a summarizing statement explain any variations you find in the pectoral and pelvic girdle for strength (rigidity); flexibility. This answer may be written as a table, naming the bones, opposite each stating its condition, and then what it affords or is adapted to.

12. What is accomplished by having two bones in the shank of the leg?

In what types or forms is there but one, and which one is it?

13. Can you a.s.sign any advantages in power, agility, length of leg, or position of leg and foot accruing from a long ankle? (See horse, frog, _et al._)

14. Enumerate the types or forms, and opposite each state the number of fingers and toes.

15. Make a table, heading one column "Form or type"; another, "Habitat"; and a third, "Habit." Judging from the structure which you see or from your previous knowledge or experience, fill in the table, stating whether the type is aquatic, terrestrial, or aerial; whether it burrows, walks, runs, or climbs, etc.

16. From your statements in 15, explain how the peculiar mode of life affects the structure of these types.

CHAPTER VII

ADAPTATIONS FOR THE PRESERVATION OF THE SPECIES

#A. METHODS OF REPRODUCTION#

1. The Simple or As.e.xual Method of Reproduction

_Materials._

Slides or diagrams, showing a dividing amba, 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.

_As.e.xual reproduction_, reproduction by division of the cell or body.

_s.e.xual 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.

_Dicious_, the different kinds of reproductive organs found in different individuals.

_Moncious_, 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 amba gained by dividing? What powers has each new cell that the original amba had lost? What would have been the fate of the amba if it had not divided into new cells?