CHAP. XIV.] THE NEOTROPICAL REGION. 81 



periods of union with the northern continent. The latest 

 important separation took place by the submergence of parts 

 of Nicaragua and Honduras, and this separation probably con- 

 tinued throughout much of the Miocene and Pliocene periods ; 

 but some time previous to the coming on of the glacial epoch, the 

 union between the two continents took place which has con- 

 tinued to our day. Earlier submergences of the isthmus of 

 Panama probably occurred, isolating Costa Eica and Veragua, 

 which then may have had a greater extension, and have thus 

 been able to develope their rich and peculiar fauna. 



The isthmus of Tehuantepec, at the south of Mexico, may, 

 probably, also have been submerged ; thus isolating Guatemala 

 and Yucatan, and leading to the specialization of some of the 

 peculiar forms that now characterise those countries and Mexico. 

 The West Indian Islands have been long isolated and have 

 varied much in extent. Originally, they probably formed part 

 of Central America, and may have been united with Yucatan 

 and Honduras in one extensive tropical land. But their sepa- 

 ration from the continent took place at a remote period, and 

 they have since been broken up into numerous islands, which 

 have probably undergone much submergence in recent times. 

 This has led to that poverty of the higher forms of life, com- 

 bined with the remarkable speciality, which now characterises 

 them ; while their fauna still preserves a sufficient resemblance 

 to that of Central America to indicate its origin. 



The great continent of South America, as far as we can judge 

 from the remarkable characteristics of its fauna and the vast 

 depths of the oceans east and west of it, has not during Tertiary, 

 and probably not even during Secondary times, been united with 

 any other continent, except through the intervention of North 

 America. During some part of the Secondary epoch it probably 

 received the ancestral forms of its Edentates and Rodents, at a 

 time when these were among the highest types of Mammalia 

 on the globe. It appears to have remained long isolated, and to 

 have already greatly developed these groups of animals, before it 

 received, in early Tertiary times, the ancestors of its marmosets 

 and monkeys, and, perhaps also, some of its peculiar forms of 



