258 ORIGIN OF LIFE IN AMERICA 



Guatemala during a residence there of several years, states 

 that the mite-fauna of Central America is composed of the 

 same genera as that of middle Europe. In some cases even 

 the species are identical. It is true that most of these genera 

 also inhabit Asia, though Linopodes, Haplophora, Nicoletiella 

 and Uropoda have not yet been recorded from that continent. 

 As some of these are known from the Oligocene Baltic amber 

 deposits, it is probable that the genera date back to at least 

 early Tertiary times. 



Of the nearly related spiders and harvestmen, Mr. Pickard- 

 Cambridge * remarks, that while the majority of the Central 

 American species are peculiar to the Nearctic and Neo- 

 tropical regions, the genera are in many cases identical with 

 those of the Mediterranean region, India, Australia or Africa. 

 There are not now in existence any land connections, he con- 

 cludes, which an arachnidal fauna could take advantage of 

 in order to pass from Africa, Australia or Europe to North 

 or South America, and we can only suggest that at some 

 period or other these now widely separated regions must 

 have been linked together by land which has long since dis- 

 appeared. 



The various groups of Central American insects are as yet 

 far from well known, and their relationships with the insects 

 of other regions have been but imperfectly determined, not- 

 withstanding the fact that Messrs. Salvin and Godman have 

 published a series of fine volumes about them. The consensus 

 of opinion of the writers, who have contributed to the 

 " Biologia Centrali-Americana," is that Central America 

 is essentially a part of South America. The purely North 

 American forms are few in number, their southern limit being 

 as a rule in Mexico. This verdict agrees also with that of 

 Dr. Calvert,f who in his recent researches on the dragon- 

 flies (Odonata) of Mexico and Central America, comes to the 

 conclusion that in the endemic as well as in the non- endemic 

 species, the South American element is much the strongest. 



Before concluding this chapter, I might again emphasize 

 the fact that the occurrences of northern genera and species 

 in Central America are almost all discontinuous. I need only 



* Pickard- Cambridge, O., " Araneida of Central America." 

 t Calvert, P. P., "Odonate Fauna of Central America," p. 467. 



