1582 THE STORY OF THE UNIVERSE 



Gaucho boys frequently run them down on horse- 

 back ana when they find no burrows or thickets 

 to escape into, they actually drop dead on the plain. 

 Probably, when they feign death in their captor's 

 hand, they are in reality very near to death. 



BIRDS. J. ARTHUR THOMSON 



BIRDS are in some ways the highest of the ver- 

 tebrate animals. They represent the climax of 

 that passage from water to land which the back- 

 boned series illustrates. Their skeleton is more modi- 

 fied from the general type than that of mammals; 

 their arrangements for locomotion, breathing, and 

 nutrition are certainly not less perfect; their body 

 temperature, higher than that of any other animals, 

 is an index to the intense activity of their general 

 life; their habitual and adaptive intelligence is fa- 

 miliarly great, while in range of emotion and sense 

 impressions they must be allowed the palm. It is, in 

 fact, only when we emphasize the development of 

 the nervous system, and the closeness of connection 

 between mother and offspring, that the mammals are 

 seen to have a right to their pre-eminence over birds. 

 Birds and mammals represent two divergent lines of 

 progress, and stand in no close connection, but the 

 affinities between birds and reptiles are sufficiently 

 marked to warrant their being included in a common 

 class (Sauropsida) , in contrast to the amphibians and 

 fishes (Ichthyopsida) on the one hand, and Mam- 

 malia on the other. Among the numerous points of 

 difference 'which separate birds from their nearest 



