- In animals, outer form and inner structure, such as:
- Number, structure and position of bones in vert. forelimb, skull
- Number and shape of teeth
- Presence or absence of feathers
- Number of Chambers in heart, number of aortic arches
- Presence or absence of placenta
- Presence or absence of ruminant stomach
In plants, leaf venation, pollen structure, arrangement of sepals, petals, bracts, cone scales, etc.