Exercise 12 - Animal Development

STUDENT OBJECTIVE

Students observe development of echinoderms, ribbon worms, and chickens. The early developmental stages in the sea star are studied and compared with more complex patterns of development. Students experimentally observe fertilization and early cleavage in sea urchins.

EQUIPMENT AMOUNT (Class of 24 with 8 groups)
Incubator, 37 ° C 1/lab
Dissecting microscope 1/student
Compound microscope 1/student
Refrigerator 1/lab


MATERIALS

Prepared slides (sharing possible to reduce costs) 1/student
  Sea star, developmental stages (CBS#E580)*
  Cerebratulus sp., developmental stages (CBS#E310)*
Sea urchins, live in pre-breeding condition; check with supplier 12/lab
    Wards #87W9030
Syringes, 5 cc 8/lab
Slides, glass and depression 24/lab
Coverslips, glass, #1 medium square 1/2 oz/lab
Pasteur pipettes 30/lab
Scissors 8/lab
Dissecting needles 16/lab
Forceps 16/lab
Paper toweling 2 pkg/lab
Beaker, 50 ml and 20 ml 8 + 8/lab
Petroleum jelly
Chicken eggs, fresh, 33, and 72 hours old (CBS#L1726)* 1 each/group
Finger bowls 2/group
Plastic wrap
Rubber bands
Developmental stages of chick--models, photographs, or plastic
    whole mounts (CBS#L1726)* Display
Bunsen burner 1/group
Glass rod, 5 mm x 10 cm 1/group
Aquarium 2/lab

SOLUTIONS

Avian Ringer's solution
Seawater
0.5 M potassium chloride (KCl)
Formalin
3.5% saline

PREPARATIONS

Several Weeks before Lab

Place an order for the sea urchins to arrive two to three days before the lab. Wards supplies an informative booklet with an order. Request that adequate seawater be shipped with the order. A local source for fertilized chicken eggs is preferred; however, supply houses do have them. Timing is critical in delivery of eggs. Check with the developmental biologist on the staff.

Week before Lab

  1. Potassium chloride preparation:
    0.5M KCl 9.3 g KCl/250 ml distilled water
    Dissolve salt in water.

  2. Avian Ringer's solution preparation:     9.0 g NaCl
    0.4 g KCl
    0.2 g CaCl2
    0.2 g NaHCO3
    Mix the salts into 750 ml distilled water and dilute to 1 liter.

Three Days before Lab

Fertilized fresh chicken eggs (8) should be placed in the incubator to supply 72-hour embryos. Place a pan of water at the bottom of the chamber to provide high humidity. Turn the eggs once or twice and spray with water.

Two Days before Lab

If time does not permit students to examine and handle the sea urchins in class, harvest gametes according to technique illustrated in the laboratory manual (fig. 12.2). Undiluted sperm will be viable for two days if kept in the refrigerator. Eggs should be kept in a small amount of seawater in the refrigerator.

33 Hours before Lab

  1. Fertilized fresh chicken eggs (8) should be placed in incubator to supply 33-hour embryos.

  2. All slides, suspensions, and equipment for observation of sea urchin fertilization should be refrigerated before lab use.

One Day after Lab

  1. The various stages of student preparations of sea urchins should be preserved with formalin.

  2. If the primitive streak is observed, preserve the fertilized egg with formalin.

NOTES

  1. Marine aquariums should be kept in a room with a constant temperature (21 ° C). Light should be diffuse; avoid bright artificial light or direct sunlight.

  2. The aquarium should be checked daily and dead sea urchins removed.

ANSWERS TO CRITICAL THINKING QUESTIONS

  1. Frog - moderate amount of yolk provides sufficient nutrition for development.
    - gas exchange occurs directly with the environment through the gelatinous coat.
    - nitrogenous wastes also diffuse directly into the environment.

    Chicken - nutrition is provided by the large amount of yolk, surrounded by a yolk sac that slowly digests the yolk and makes the nutrients available to the embryo.
    - gas exchange occurs through the chorion, an extraembryonic membrane lining inside of the shell.
    - nitrogenous wastes are stored in the allantois, a sac produced from the allantoic membrane. This membrane also provides a respiratory surface.

    Humans - nutrient uptake, gas exchange and waste removal is all performed by the placenta, a complex organ arising from the growth of chorionic villi into the surface of the uterus.

  2. After gastrulation in a sea star, differentiation produces a small, sexually immature free-swimming larva. This feeding stage continues to grow and at a later stage will metamorphose into a miniature version of an adult sea star.
         Gastrulation in the chick is followed by neurulation and organogenesis, resulting in a sexually immature, miniature version of the adult form. Note that there is no intermediate, larval stage.

SUPPLEMENTAL MATERIALS

Bio Sci II, videodisc--contains sequences on frog and sea urchin development. Dubuque, IA: Wm. C. Brown Publishers. See appendix.

The Chick Embryo--from Primitive Streak to Hatching, 13-minute film. Chicago, IL: Encyclopaedia Britannica Educational Corp.

Chick Embryology, 35 mm set. Burlington, NC: Carolina Biological Supply. #48-1269M

Fish Embryology, 21-minute VCR of Geisha girl fish development from egg to hatching stage: Concord, N.H., Essayo.

Introduction to Development, (NC1658) an award-winning VCR examining development of chick and frog. Bloomington, IN: Indiana University Audio-Visual Center.

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