444 CLASS MAMMALIA. 



is fully developed towards the fifth year. The Wild Horse 

 may live from thirty to forty years. In youth, the age is 

 known by the incisors : these teeth have a hollow in their 

 upper part, which is gradually effaced by use, and the de- 

 grees are so regular as to correspond with a determinate 

 space of time. 



The milk-incisors are whiter and narrower than those 

 which follow. At about fifteen months old, those which 

 first appeared begin to lose their cavity by the effect of 

 wear. Those which come after are not marked until the 

 twentieth month. Finally, after two years, the cavity of 

 these last is in its turn effaced ; the adult teeth lose their 

 cavities in a similar order. Any differences in these va- 

 rious changes are characteristic of peculiar races, and 

 sometimes of individuals which arrive sooner at the adult 

 state. After the twelfth year there are no certain rules to 

 judge of the age of Horses. 



The wild troops have no fixed place of repose ; they 

 usually select dry and sheltered situations for that purpose, 

 at the foot of a rock for example, or the edge of a wood, 

 where they may be protected from the winds. They have 

 the same dread of storms that most other animals have. 

 At the approach of the tempest they are agitated and rest- 

 less ; they seek the wildest and most sequestered spots to 

 conceal themselves. If the storm bursts forth before their 

 retreat, if a violent clap of thunder should be heard, the 

 terrified troop betakes itself to instantaneous and rapid 

 flight ; the wind and the lightning cannot outstrip them. 

 Wretched indeed would be the living object that should 

 intercept them in their route. 



The mothers which have young ones never quit the 

 troop ; these last are courageously defended by the rest, 

 and rarely fall by the tooth of any carnivorous animal. If 

 the enemy is formidable, and they cannot escape, they 

 unite in a close and circular band, approach their heads 



