I. Levels of Organization
Cell
Æ
Tissue
Æ
Organ
Æ Organ System
II. Symmetry:
A. Spherical – any plane passing through the center divides
body into equal halves E.g. Volvox
B. Radial - body divided into similar halves 2 or more planes
passing through a longitudinal axis
E.g. jellyfish (Cnidaria) &
sea stars (Echinodermata)
Ö if you divide into “pie pieces” each piece
contains roughly the same structures
C. Bilateral - divided head to tail, one side of the body
mirrors the other
1. Demonstrates forward movement
2. Cephalization = concentration of nervous tissue &
sense organs in the anterior end of the body
1
III. Body Language
A. Anterior – “head” end
B. Posterior – “tail” end
C. Dorsal – spine side
D. Ventral – belly side
E. Medial – towards the midline
F. Lateral – towards the sides
G. Distal – far away from the point of attachment
H. Proximal – close to the point of attachment
I. Pectoral – chest region
J. Pelvic – hip region
K. Cephalic – “head” area
2
Note: One has to think a little to apply these to humans,
since we are only bi-pedal !
3