SCIENCE AND TRAVEL 205 



America, he noticed one species replacing another, 

 perhaps closely allied, species. Of the carrion-feed- 

 ing hawks the condor has an immense range, but 

 shows a predilection for perpendicular cliffs. If an 

 animal die on the plain the polyborus has preroga- 

 tive of feeding first, and is followed by the turkey 

 buzzard and the gallinazo. European horses and cat- 

 tle running wild in the Falkland Islands are some- 

 what modified ; the horse as a species degenerating, 

 the cattle increasing in size and tending to form 

 varieties of different color. The soil being soft the 

 hoofs of the horse grow long and produce lameness. 

 Again, on the mainland, the niata, a breed of cattle 

 supposed to have originated among the Indians south 

 of the Plata, are, on account of the projection of the 

 lower jaw, unable to browse as effectually as other 

 breeds. This renders them liable to destruction in 

 times of drought. A similar variation in structure 

 had characterized a species of extinct ruminant in 

 India. 



How disastrous a great drought might prove to 

 the cattle of the Pampas is shown by the records of 

 1825 and of 1830. So little rain feU that there was 

 a complete failure of vegetation. The loss of cattle in 

 one province alone was estimated at one million. Of 

 one particular herd of twenty thousand not a single 

 one survived. Darwin had many other instances of 

 nature's devastations. After the Beagle sailed from 

 the Plata, December 6, 1833, vast numbers of but- 

 terflies were seen as far as the eye could range in 

 bands of countless myriads. " Before sunset a strong 

 breeze sprung up from the north, and this must have 

 caused tens of thousands of the butterflies and other 



