ZOOLOGICAL POSITION 3 



whole group ; the claws are sharper and curved 

 into strong hooks more than in any other mam- 

 mal, and by the action of special muscles are 

 withdrawn under the protection of sheathlike 

 pads, that they may escape wear and injury 

 when not in use ; 110 teeth are better fitted for 

 their work the great canines for tearing, 

 and the scissor-like premolars for shearing off 

 lumps of flesh small enough to swallow ; while 

 the short and simple alimentary tract takes up 

 little internal space, and permits of a lithe and 

 slender form suited to the highest activity, at 

 the same time performing its digestive work 

 rapidly, and soon ridding the animal of the bur- 

 den of the enormous meals which those which 

 feed only when tlkey can are certain to indulge 

 in when the opportunity arises. In the eye, 

 the fibres of the iris, opening to the widest ex- 

 tent, expand the pupil to a full circle, admit- 

 ting every ray of light which can fall upon it 

 during the darkness of night, and by a rapid 

 and spontaneous contraction in some species 

 to a narrow slit, in others to a ring as small 

 as a piiihead shut off all excess of blinding 

 light at midday, and permit minute exactness 



