A Guide for the Study of Animals Part 7

_Regions_, princ.i.p.al divisions of the body of an animal.

_Head_, _thorax_, and _abdomen_, the three distinct regions into which the body of a gra.s.shopper is divided.

_Somite_, a ring-like division of the body of an animal.

_Prothorax_, _mesothorax_, and _metathorax_, the three divisions or somites into which the thorax of any insect is divided. A pair of legs is borne on each division.

_Exoskeleton_, an external skeleton.

_Femur_, _tibia_, and _tarsus_, the three princ.i.p.al divisions of the leg corresponding to thigh, shank, and foot.

_Veins_, thread-like thickenings of the wings.

_Ocelli_, the single or simple eyes of an insect, composed of a single eye element.

_Compound eyes_, made up of many eye elements.

_Auditory sacs_, organs for hearing in many animals.

_Antennae_, the feelers borne on the head.

_Labrum_, the upper lip.

_Labium_, the lower lip, formed by the growing together of the second maxillae.

_Mandibles_, primary jaws situated under the labrum.

_Maxillae_, secondary jaws just in front of the labium, each composed of three parts, a palp, a spoon, and a tooth.

_Palps_, the jointed finger-like structures used to handle food, one pair on the labium and one pair on the maxillae.

_Spiracles_, openings into the trachea found along the sides of the abdomen and thorax.

_Tracheae_, slender tubes used for breathing organs among insects.

They carry the air direct to the tissues in all parts of the body.

_Ovipositors_, structures on the posterior end of the abdomen of a female, used to deposit eggs.

_Metamorphosis_, refers to the development of the young of animals when striking changes in structure occur in the course of their growth. Metamorphosis is called _complete_ when the young have no resemblance to the adults, and _incomplete_ when there is a resemblance to the adult. In complete metamorphosis the stages are _larva_, _pupa_, and _adult_. In incomplete metamorphosis the stages are _nymph_ and _adult_.

_Observations._

_The Body._

1. Show how the shape of the gra.s.shopper's body is well adapted to its needs.

2. Which region of the body is the thickest? What seems to be the reason for this? Which regions are capable of movement?

_Locomotion._

3. What are the various kinds of locomotion a gra.s.shopper can use?

Which are used in the vivarium and which when free in the laboratory?

4. Which legs are used in jumping? How are these legs especially adapted to this, in length, structure and direction? Could a gra.s.shopper jump if the third pair of legs were arranged like the other two pairs? Why?

5. How is the animal able to cling to gra.s.s stems and not slip down?

What is the direction of the body in relation to the stem or gra.s.s blade?

6. What is the position of the wings when at rest? when in use? How do the hind wings fold? How are the princ.i.p.al veins of the wings arranged to permit or facilitate this folding?

7. Contrast the fore and hind wings with respect to thickness, size, and use.

8. To which somites of the thorax are the wings attached? Nearer which surface, the dorsal or ventral? Why?

_Sense Organs._

9. Discover all you can about the uses of the antennae by carefully observing gra.s.shoppers at rest, feeding, jumping and crawling, approaching an object or another gra.s.shopper, etc.

10. How many compound eyes has the gra.s.shopper? How many simple eyes?

Where are they located?

Examine a preparation of the compound eye with the low power or as demonstrated with the stereopticon. What is the shape of an eye element of the compound eye? About how many eye elements are there in a compound eye?

_Feeding._

11. Do gra.s.shoppers eat and drink while in captivity? Put a fresh bunch of gra.s.s which has been sprinkled with water in a vivarium with gra.s.shoppers that have had no food or drink for twenty-four hours and watch results.

12. What is the position of the gra.s.shoppers in feeding? In what direction do the jaws move in feeding? Compare this with the direction of movement of your own jaws. What is the use of the palps?

What do you think is the use of the "mola.s.ses" or saliva that flows from the mouth?

_Respiration._

13. Describe the breathing movements of a gra.s.shopper and explain the relation of the movements to inhalation and exhalation of air.

14. Find the exact location and number of spiracles on the abdomen.

There are two pairs of spiracles on the thorax. Find them. How do the spiracles prevent the entrance of dust?

Describe a trachea as seen in a mounted preparation with the aid of a microscope or stereopticon.

_Protection._

15. Explain how the colors of the gra.s.shopper may be protective or useful when at rest in its natural habitat and when in flight.

16. Does the sh.e.l.l cover the entire body? What are the advantages of such a covering? A sh.e.l.l is likely to hinder activity, sensitiveness, and growth. How are such disadvantages overcome in this case?

17. What senses are probably most relied upon to detect approaching danger? Give evidence to support your answer.

18. What is the position of the hind legs when at rest? What relation has this to safety?