276 STUDIES, SCIENTIFIC AND SOCIAL chap. 



subject of allied forms occurring in the tropics of both 

 hemispheres. Besides the barbets (Megalsemidse) which 

 occur in the tropics of Asia, Africa, and America in almost 

 equal abundance, we have the trogons, abundant in Asia 

 and America, but with a single peculiar genus of two species 

 in Africa, and the tapirs confined to the Malay islands 

 and tropical America ; while equally remarkable are two 

 genera of snakes, Dryiophis and Dipsadoboa, confined to 

 West Africa and tropical America. Towards an ex- 

 planation of these curious anomalies we have the very 

 interesting fact, that tapirs closely resembling those now 

 living abounded in Europe during the Miocene period, 

 and continued to live in the Pliocene period, both in 

 France and England, as well as in North America. This 

 suggests that a tropical climate is not essential to these 

 animals, and that their present restricted range is due to 

 other than climatal causes. We may also be sure that if 

 they could live so far north as our island in the Pliocene 

 period, they might have ranged considerably further north 

 during the earlier and warmer Miocene. The only 

 difficulty is, how did these Miocene tapirs reach America ? 

 and if we can find any reasonable answer to this question 

 we may consider that it will equally apply to all the other 

 cases which have been mentioned. 



The close relation between many of the extinct mam- 

 malia of North America and Europe at successive periods, 

 while in other cases entire groups have always been 

 restricted to one continent only, renders it certain that 

 there existed at several distinct epochs some land con- 

 nection sufficient to enable terrestrial animals to pass 

 between them. The sea at Behring Strait is so shallow 

 that we may safely conclude that the continents of Asia 

 and America have here been recently connected, while the 

 shallow Okhotsk, Japan, and Yellow seas indicate a large 

 extension of the lowlands of Eastern Asia ; but the very 

 deep ocean comes up to beyond 55° N. latitude on the east 

 side of Kamschatka, so that this part of the connecting 

 land would probably always have had a warm temperate 

 rather than a tropical climate. On the European side 

 we find between the west of Ireland and Newfoundland a 



