(Source : http://www.google.co.in/search?hl=en&q=Blister+pack&bav=on.2,or.r_gc.r_pw.r_qf.&biw=
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Cg#um=1&hl=en&tbm=isch&sa=1&q=Ball+%26+Socket&oq=Ball+%26+Socket&gs_l=img.12...66.
11704.14.13851.14.13.0.0.0.0.0.0..0.0...0.0...1c.dXuxHy3cwsE&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf
.&fp=da2754da80a3320d&biw=1328&bih=574 ; Aug 9, 2012)

Skin- An outer layer or set of layers on animal, plant, or mechanical device that serves to enclose that protect its contents. Skin is the soft external covering of skeletons (plate 29A). The covering with external membrane may drastically vary from one living being to another.  Snails have different covering structure and chemical composition that is hard as the protection shelter. Human skin is a sensory organ sensitive to heat, touch, moisture, etc. The skin is one of the most important parts of the body because it has the first line of defence from external factors. For example, the skin plays a key role in protecting the body against virus and excessive water loss, insulation, temperature regulation, sensation, and the production of vitamin. Skin can be separated from the flesh.

Other animals have fur (plate 29C) which is constructed with dense hair. Primarily, fur increases the insulation the skin protects from outer temperature. Interestingly skin serve as a secondary sexual characteristic. In Indian sub-continent fair-skin carries special attraction compare to darker skin. Skin can help in camouflaging from the prey. On some animals, the skin is very hard and thick (plate 29D), and can be processed to create leather. Reptiles and fish (plate 29 D&E) have hard protective scales on their skin for protection, and birds (plate 29B) have hard feathers,

Plate 29A Human Skin (Soft & Tender)	29B Bird Feather	29C Lion fur     (Fur)	29D Crocodile Skin  (Hard Skin)	29E Fish   (Scale)