12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



Occurring originally as a uniform or slightly varying organism 

 over a land including the Malayan region (but not the Australian), 

 central Africa, and northern South and Central America, the original 

 prototype of the family became differentiated, taking on the aspect in 

 which we see it today, by the following processes : 



The increasing height of the Andes, besides enabling the species 

 living in that region to maintain themselves in the most suitable 

 temperatures, isolated at a very early epoch such individuals as were 

 living west of their crest, rendering them secure from invasion by 

 types of later origin economically more specialized, and fitted to oc- 

 cupy a habitat with a slightly higher average temperature. 



A new type, an immigrant from the east, better equipped econom- 

 ically than the original type and with a slightly higher optimum 

 temperature, reached Africa, northern South and Central America, 

 overrunning and extirpating the original type from all the territory 

 east of the crest of the Andes and later in a few places even invading 

 the mountainous region itself. This type subsequently became locally 

 differentiated, through the same" processes by which it itself was 

 originally evolved, into five subtypes, the three newer, more special- 

 ized and more efficient, extirpating the original immigrant (their 

 immediate ancestor) wherever they were able to reach it. 



But before the differentiation of this type into subtypes, though 

 subsequent to the extension of its range westward as far as the 

 Cordillera, Africa became separated from the Malayan region and, 

 at about the same time, also from South and Central America, this 

 latter process involving the submergence, or disruption from other 

 causes, of the Antillean region, resulting in the formation of the West 

 India archipelago. 



So far as we know at present no representative of the original 

 immigrant type remains in Africa, though it is quite possible that 

 some eventually will be found there. Its single known derivative in 

 this region, Mesoperipatus, though very different, approaches the 

 Malayan type more closely than do any of the American types. 



This may be due to either of two causes ; southern India and Ceylon 

 maintained a connection with Africa after their separation from the 

 Malayan region, and it is possible that this more efficient type reached 

 this region in or near its present form from the Malayan region just 

 before the separation of the two, subsequently spreading to Africa, 

 but being prevented from extending its range to America by the for- 

 mation of the Atlantic Ocean ; or, which is far more likely, these three 

 types may be all of local development, the African approaching more 



