Laboratory work 5
The aim of the fifth laboratory is to see the directions of evolution in vertebrates and tell aromorphoses from idioadaptations. Wet specimens of a fish and an amphibian and models or pictures of a reptile, bird and mammal are used. First the structure of each class is studied and an aromorphosis is written in the table: in fish the gill, fins and two-chambered heart; in amphibians lungs, a three-chambered heart and five-toed limbs; in reptiles dry horny skin, internal fertilisation and the amniotic egg; in birds the four-chambered heart, feathers, air sacs and warm-bloodedness; in mammals hair, uterus, mammary glands and a developed brain. Then one species of each class is chosen and its idioadaptation found: the electric ray stuns prey with electric organs, the green frog lives on water and land thanks to moist skin and long hind legs, the Central Asian tortoise is protected by a hard shell, the white stork looks for food in shallow water with long legs and bill, and the blue whale feeds on plankton with a blubber layer and baleen plates instead of teeth. Conclusion: aromorphoses separate classes, idioadaptations fit species to a particular environment.
Fill in a table from pictures or models: class, aromorphosis, species, idioadaptation. If there are no wet specimens, work from pictures. Safety: do not handle wet specimens without gloves; do not inhale or taste the preservative (formalin); wash hands afterwards.