We're trained as children to think in terms of 'shape'. This is one of the things you have to overcome when learning to be an artist. Seeing shape is fine for some things, but observed drawing is best done in terms of form instead of shape. Shape is a 2D abstraction, form is seeing in 3d - with depth and volume. To finish out perspective week this video provides an exercise to help you envision form. All you need to do is go find some cool pictures of bugs!
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Assignment: Overlay form lines onto photos of interesting bugs.
Things to consider: Draw through the object, envision the structure.