1. Embryo Lab

2. Why did your order the drawings the way you did? Please list the traits you observed that caused you to put the embryos in the order that you did.

3. What similarities do the drawings have? Similarities include similar eyes, tails and visible spinal cords. Notice that each embryo develops a tail, buds that become limbs and pharyngeal pouches (which house the gills of fish and amphibians).

4. What are the differences? Students should list and discuss differences in size and shape of the embryos.

5. What trends do you see as you go from stage to stage? Although vertebrate bones are homologous, limbs develop differently in each group. The tail remains in most adult vertebrates. Although the coccyx (tail bone) serves as a point of attachment for certain muscles, this small internal tail does not resemble the long external tail of most other vertebrates. In humans the tail and pharyngeal pouches are relics (forms from the past) that disappear before birth.

6. And now…. …the moment you have all been waiting for… …the moment of truth. How many pictures do you think you have in the correct spot?

7. Order of Embryos from earliest to latest in development. FishChickenPigCalfHuman Stage 1823104 Stage 21761511 Stage 314913125

8. What was the purpose of this activity? Early in development, all vertebrate embryos are remarkable similar. These relics and the similarities among the embryos strongly suggest that the development of all vertebrates evolved as new genetic instructions were layered on top of older ones.