This was a puzzle that a friend sent me (not sure of the origin).  I
can't for the life of me figure out any pattern, let alone solution. 
The puzzle is 9 boxes - 8 are filled with shapes/figures and the 9th
is empty box.  There are 5 possible solutions for the 9th box listed.
See puzzle at below url...

http://www.crabwise.com/puzzle.jpg

I think the answer should be 2.

Now, I will "try" to explain!

Going Left to right 
New item introduced in the second box (compared to first) remains intact in box 3

in row 1  it is the line, row 2 is square so, row 3 should have a + sign

Top to bottom is a bit tough, I can only find that there is a shap in
second row that can conver to a shap in Row 3.

Verticle Elipse converts to Straignt line, the center squar can
convert to the + sign
so on that logic the square should conver to circle.

Hope this works.

I'll through in my two cents here, but the bottom line is...who the
hell really knows!

Going across each row, there is a decreasing number of enclosed spaces.

Row 1 starts with three enclosed spaces on the left, then one, then none.

Row 2 goes from 7 to 3 to 1.

Row 3 starts with 2, then 1, so the last box would need to be zero
enclosed spaces, which means that solution #1 is te only one that
works.

Or maybe not....

I like No. 1 for a different reason.  
Looking at the corner boxes.  The top right is the bottom left
dis-assembled. So, the bottom right should be top left dis-assembled. 
The other five boxes are just distractions.
Libby

I suspect it of being a parody with no correct answer.

Archae0pteryx

I say 3, the triangle.
  
Solution 1 is a modification of the figure in box 3, top row - the
intersecting arcs are wrongly positioned and a line is missing.
  
Solution 2 is a modification of the figure in box 2, bottom row - the
cross is not in the same position.
  
Solution 4 is a modification of the figure in box 1, bottom row  - a
line is missing and the other object is not a circle, it is
oval-shaped.
  
Solution 5 is a modification of the figure in box 3, middle row -
another square has been superimposed on the original.
  
I propose Solution #3, because 
a) the triangle shape does not appear in the puzzle
b) every other solution includes shapes that appear in the puzzle, but
each one has been modified to some degree.
  
The triangle is the only shape that has *not* been modified, and
therefore it should be the solution.

Oh, my!  I think jackburton is right.  To put it another way, all
options but the triangle represent a partial duplication of another
shape.  Only the triangle can be added to the set while allowing each
shape in the completed set to remain unique.

Jack, if this were my question, I'd be inviting you to post the answer.

Archae0pteryx