400 LAND ANIMALS 



the large insects occurring in the cold regions are always small in 

 comparison with the tropical forms and are mostly relicts of a warmer 

 period.* Myriapods may become 28 cm. long (Spirotreptes seychel- 

 larum) ; among the scorpions, tropical forms, such as Pandinus impera- 

 tor, attain a length of more than 17 cm., and the Javan bird-catching 

 spider (Selenocosmia javanensis) becomes 9 cm. long. The land snails 

 in the tropics are also of a much greater weight than those in temperate 

 climates. The shell of Achatina schweinfurthi from Africa becomes 171 

 mm. high, that of Bulimus garcia-moreni from Ecuador measures 147 

 mm. in height and 85 mm. in width, and the animal lays eggs 51 by 

 35 mm., as large as those of a hen; many helicids, like Pyrochilus 

 lampas of the Moluccas and Pleurodonta gigantea of the Antilles, also 

 attain a large size; tropical species of the limacid genus Vaginula may 

 oe 20 cm. long when extended. Amphibia thrive better in the tropics 

 than elsewhere; the largest frog, Rana goliath, with a body length of 

 250 mm., lives in South Cameroon. Reptiles are nowhere as large as 

 in the tropics. The crocodiles are at home there; the giant tortoises are 

 confined to the tropics; large iguanas and boas live in tropical America, 

 and monitors and pythons in Asia and Africa grow to gigantic size. 



The above does not apply to the homoiothermal animals ; they bear 

 optimal conditions within themselves, and universally live in a 

 physiologically tropical climate. They can attain large sizes in the 

 temperate zones. It is true that the largest bird, the ostrich (Struthio) , 

 is at present an inhabitant of the tropics and subtropics; but the 

 powerful moas of New Zealand, that surpassed it in size, lived in tem- 

 perate climates, and other birds of great size, like the condor, the 

 American rhea, the large penguins (Aptenodytes) , and the extinct 

 great auk, are inhabitants of cooler climates. The elephant is the largest 

 land mammal now living, but the mammoth that lived even in arctic 

 regions in the post-glacial period was approximately as large. 



Much has been written about the beautiful coloration of tropical 

 animals, but the hypothesis that this phenomenon may be due directly 

 to climatic conditions remains to be proved. The tropical genera of 

 birds are striking to us both because of individual brilliancy of color 

 and variety of color pattern, but the proportion of brilliant forms in 

 the whole fauna remains approximately the same as in temperate 

 regions, since the number of dull-colored forms in the tropics is like- 

 wise increased 76 (see also Chapter XXVI). The notion that there are 

 no good singers among the singing birds in the tropics is emphatically 

 contradicted by many travelers (Wallace, Darwin, Bates, Sarasin, and 



* Mantis, Locusta, Lucanus, Saturnia. 



