354 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



mass. By its means such animals as the camel and the horse, both 

 of which first developed in North America, and subsequently be- 

 came extinct in that continent, arrived in Asia, the horse passing on 

 to Europe, where it became the servant of man, and was subse- 

 quently reintroduced into America by him. 



When we come to examine the distribution of the cold-blooded 

 vertebrates, such as reptiles and fishes, we have to go further back 

 in the geological history of the country in order to understand its 

 significance, and it is here that our want of knowledge is most keenly 

 felt. Nevertheless, a few interesting facts may be culled from what 

 we already know, facts which throw a certain amount of light upon 

 the subject. 



An examination of the map of the Old World will reveal the fact 

 that a desert belt stretches from Morocco in North Africa right 

 across Asia to the borders of Manchuria, where it stops within a 

 hundred miles or so of the sea. It has been suggested that it was 

 this desert belt, known to be of considerable age, that prevented the 

 Urodela, or tailed amphibians, from spreading south from Europe 

 and north Asia into Africa and India. Force is given to this con- 

 tention by the fact that it is only in the extreme eastern part of 

 their range in Eurasia that they occur south of the desert belt in 

 question, for there they found a stretch of humid country by 

 means of which they could spread southward with safety. It is 

 easy to see how such animals as newts and salamanders, which de- 

 pend entirely upon the presence of ponds, streams, or lakes, wherein 

 to lay their eggs and where their young develop, and which them- 

 selves can not exist in any but a humid environment, would find it 

 utterly impossible to cross a stretch of dry, sandy desert. 



Incidentally it may be mentioned that another animal that appears 

 to have been influenced in its distribution by this desert belt is 

 the roedeer (Capreolus), whose range extends from the extreme west 

 of Europe throughout that continent, central Asia, north of the 

 deserts, and Siberia into Manchuria. Thence it turns south and west, 

 extending into north China and on into eastern Tibet. This deer 

 does not occur in central or south China, its range being bounded 

 in this direction by the Tsing Ling Mountains. 



Reptiles represent a very old group of animals. One instance in 

 connection with their ancestry and distribution may be mentioned 

 here. It is that of the little Yangtse alligator. The Crocodilidce 

 represent almost the very oldest living group of reptiles, and they 

 acquired their distribution upon the face of the earth a very long 

 time ago. It is believed that they originated in the Old World, 

 spreading into the New World at a verv remote period. These 

 New World members of the group are mainly alligators or caimens, 



