76 ANIMAL LIFE 



outwards by the set of the ciliary current, which, as we 

 saw, maintains an outgoing flow. The ' turbinals, 5 as 

 these labyrinths are called, help in other ways, by 

 warming and scenting the air, and serve to build up 

 the long and stout face that distinguishes herbivorous 

 animals. 



Another means of rendering the food easily 

 digestible is known as chewing the cud. The cud is 

 not the herbage taken straight from the field, but 

 consists of a mass of pulpy grass which has undergone 

 partial digestion, and has been sent back into the 

 mouth for a thorough mastication. All animals with 

 a cloven hoof, except pigs, are ruminants, whilst 

 those which have more than two complete toes or only 

 one, are not provided with this singular mechanism. 



Among the birds, devices of a much less complex 

 kind are adopted for obtaining a vegetarian diet. 

 But few birds subsist on leaves, for their innutritious 

 character makes it necessary to gather large supplies 

 in order to furnish even a small amount of food, and 

 then it is only obtained at the expense of much hard 

 mastication. For a bird such a diet is eminently 

 unsuitable, since it neither wishes to overweight itself 

 with a heavy meal nor has it teeth to grind with. 

 Unlike the ruminants, which graze in safety, most 

 birds appear perpetually harassed by real or imaginary 

 fears, and need a light, stimulating diet to replace the 

 great loss of material and energy which they expend 

 in active, sustained movement, and many other 

 ways. For them, therefore, oil, starch, and other 



