The Headwaters of the Paraguay 123 



prey and those that are preyed on, concealing coloration 

 has not been a survival factor; throughout the ages dur- 

 ing which they have survived they have gradually lost 

 whatever of concealing coloration they may once have 

 had — if any — ^and have developed a coloration which 

 under present conditions has no concealing and perhaps 

 even has a revealing quality, and which in all probability 

 never would have had a concealing value in any "envi- 

 ronmental complex" in which the species as a whole lived 

 during its ancestral development. Indeed, it seems as- 

 tonishing, when one observes these big beasts — ^and big 

 waders and other water-birds — in their native surround- 

 ings, to find how utterly non-harmful their often strik- 

 ingly revealing coloration is. Evidently the various 

 other survival factors, such as habit, and in many cases 

 cover, etc., are of such overmastering importance that 

 the coloration is generally of no consequence whatever, 

 one way or the other, and is only very rarely a factor of 

 any serious weight. 



The junction of the Sao Louren^o and the Paraguay 

 is a day's journey above Corumba. From Corumba 

 there is a regular service by shallow steamers to Cuyaba, 

 at the head of one fork, and to Sao Luis de Caceres, at 

 the head of the other. The steamers are not powerful 

 and the voyage to each little city takes a week. There 

 are other forks that are navigable. Above Cuyaba and 

 Caceres launches go up-stream for several days' journey, 

 except during the dryest parts of the season. North of 

 this marshy plain lies the highland, the Plan Alto, where 

 the nights are cool and the climate healthy. But I wish 

 emphatically to record my view that these marshy plains, 



