GENERAL LIFE OF MAMMALS. 639 



ship. At the breeding season, a remarkable organic reaction 

 often affects the animal, the timid hare becomes a fierce 

 combatant, and love is often stronger than hunger. The 

 courtship of Mammals is usually like a storm violent but 

 passing : for, after pairing, the males return to their ordinary 

 life, and the females become maternal. Some monkeys 

 are faithfully monogamous ; and exceptional pairs, such as 

 beavers and some antelopes, remain constant year after year; 

 but this is not the way of the majority. 



The duckmole lays eggs and brings up her young in the 

 shelter of the burrow ; the Echidna has a temporary pouch. 

 In Marsupials the time of gestation is very short, and there 

 is no truly placental union between the unborn young and 

 the mother. The new-born Marsupials are very helpless, and 

 are in most cases transferred to an external pouch or 

 marsupium, within which they are nurtured. In Placental 

 Mammals the gestation usually lasts much longer than in 

 Marsupials, its duration varying to some extent with the 

 rank in the mammalian series, but there are great differences 

 in the condition of the young at birth. " In those forms," 

 Professor Flower says, " which habitually live in holes, like 

 many Rodents, the young are always very helpless at birth ; 

 and the same is also true of many of the Carnivora, which 

 are well able to defend their young from attack. In the 

 great order of Ungulates or Hoofed Mammals, where in the 

 majority of cases defence from foes depends upon fleetness 

 of foot, or upon huge corporeal bulk, the young are born in 

 a very highly developed condition, and are able almost at 

 once to run by the side of the parent. This state of relative 

 maturity at birth reaches its highest development in the 

 Cetacea, where it is evidently associated with the peculiar 

 conditions under which these animals pass their existence.' 7 

 The importance of prolonged infancy, as illustrated among 

 monkeys, should be recognised in connection with the evolu- 

 tion of sympathy. 



The maternal sacrifice involved in the placental union 

 between the mother and her "foetal parasite," in the pro- 

 longed gestation, in the nourishment of the young on 

 milk, and in the frequently brave defence of the young 

 against attack, has been rewarded in the success of the 

 mammalian race, and has been justified in the course of 



