72 THE DESCENT OF MAN. [Part L 



cial animals perform many little services for each- other : 

 horses nibble, and cows lick each other, on any -spot which 

 itches: monkeys search for each other's external para- 

 sites ; and Brehm states that, after a troop of the Cerco* 

 pithecus griseo-viridis has . rushed through a thorny 

 brake, each monkey stretches itself on a branch, and 

 another monkey sitting by " conscientiously " examines 

 its fur and extracts every thorn or burr. 



Animals also render more important services to each 

 other : thus wolves and some other beasts of prey hunt 

 in packs, and aid each other in attacking their victims. 

 Pelicans fish in concert. The Hamadryas baboons turn 

 over stones to find insects, etc. ; and when they come to a 

 large one, as many as can ptand round, turn it over to- 

 gether and share the booty. Social animals mutually de- 

 fend each other. The males of some ruminants come to 

 the front when there is danger and defend the herd with 

 their horns. I shall also in a future chapter give cases of 

 two young wild-bulls attacking an old one in concert, and 

 of two stallions together trying to drive away a third 

 stallion from a troop of mares. Brehm encountered in 

 Abyssinia a great troop of baboons which were crossing 

 a valley : some had already ascended the opposite moun- 

 tain, and some were still in the valley : the latter were at- 

 tacked by the dogs, but the old males immediately hurried 

 down from the rocks, and with mouths widely opened 

 roared so fearfully, that the dogs precipitately retreated. 

 They were again encouraged to the attack ; but by this 

 time all the baboons had reascended the heights, except- 

 ing a young one, about six months old, who, loudly calling 

 tor aid, climbed on a block of rock and was surrounded. 



Hamadryas turning over stones, the fact is given (s. 76) on the evidence 

 of Alvarez, whose observations Brehm thinks quite trustworthy. For the 

 cases of the old male baboons attacking the dogs, see s. 79 ; and, with re- 

 spect to the eagle, s. 56. 



