(Read more: http://en.wikipedia.org/wiki/File:Fibonacci_spiral.svg ; Aug 4, 2012)

A spiral continually changes in radius (plate 16B). The change might be linear, increasing at a constant rate, or the rate of change itself might increase at a steady rate, in which case we call it logarithmic spiral. A linear increasing radius can be demonstrated by winding a rope into a spiral. A logarithmic spiral can be seen on the underside of most snail shells (plate 17A).

Plate 17A Spiral Snails		17B Centipede	17B CD Track

(Source : http://www.google.co.in/search?hl=en&q=Spiral+snails&bav=on.2,or.r_gc.r_pw.r_qf
.&biw=1328&bih=574&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=1cAcUPucB
ofOrQeS-YD4AQ ; Aug 4, 2012

Plate17A&B : http://www.google.co.in/search?hl=en&q=Spiral+in+nature&bav=on.2,or.r_g
c.r_pw.r_qf.&biw=1328&bih=574&um=1&ie=UTF8&tbm=isch&source=og&sa=N&tab=wi&ei=
6DkdUJO3Dc3orQf3n4CgDg#um=1&hl=en&biw=1328&bih=574&tbm=isch&sa=X&ei=yDodU
OLiJcvNrQeKqoDgAQ&ved=0CEMQvwUoAQ&q=Spiral+in+centipede&spell=1&bav=on.2,or
.r_gc.r_pw.r_qf.&fp=dd0db88348be4c18 ; Aug 4, 2012)

Human beings have applied the mechanism of spiral quite efficiently for various purposes. The spiral formation among insects is very effective defence mechanism that makes a compact body (plate 17B) and protects from possible prey. Snails under threat from the prey contract their body inside the hard spiral-shell so that prey cannot reach easily inside. By forming spiral formation centipede create a much stronger compact body-structure from any outside threat (plate 17B). A spiral is a good way to compact
something that would otherwise be long. Thus, as mentioned in the disc paradigm, something like a music CD (plate 17B) contains a linear track of information, nearly five miles in length. Traditional audio records have the spiral engraving record of the sound track.