NO. I DISTRIBUTION OF THE ONYCHOPHORA — CLARK 5 



THE DISTRIBUTION OF THE PERIPATIDtE 



The distribution of the species of Peripaticke indicates that, so far 

 as the onychophores are concerned, Sumatra and the Malay Pen- 

 insula, central Africa and tropical America collectively form a 

 zoogeographical unit. 



This agrees with what we conclude from the distribution of other 

 types, most of which, however, fall into two groups, an Afro-Amer- 

 ican and an Afro-Malayan. 



No onychophores have as yet been reported from southern India. 

 On the basis of what we know of other forms we would expect in 

 this region a genus or genera more closely related to African than to 

 Malayan types. 



Of the genera inhabiting the zobgeographic area under considera- 

 tion Eoperipatus (belonging to the subfamily Eoperipatinse) of 

 Sumatra and the Malay Peninsula shows the highest degree of 

 specialization, and is rather abruptly differentiated from the remain- 

 ing three genera, which collectively form a distinct systematic unit 

 (the Peripatinse) . 



Mesoperipatus of central Africa is considerably less specialized 

 than Eoperipatus, though more specialized than Peripatus of eastern 

 South and Central America, which in its turn is more specialized than 

 the very primitive and worm-like Oroperipatus of South and Central 

 America west of the crest of the Andes. 



EXPLANATION OF THE DISTRIBUTION OF THE PERIPATID^ 

 In order that the facts brought out by the geographical distribution 

 of the genera and species of the Peripatidse may be understood, it is 

 necessary first to give a brief sketch of the processes by which the 

 geographical differentiation of animals is brought about. 



The physical and economic conditions under which any new animal 

 type arises are naturally the optimum conditions for the perpetuation 

 of that type in its original form, and the generative center, or the 

 center of distribution, of the type will be the locality where the 

 optimum conditions represent the average or mean of a long range of 

 imperceptibly varying conditions, representing all of the conditions 

 under which it is possible for the type to exist, and therefore per- 

 mitting of progressive deviation from the original type through 

 gradual adaptation for a maximum distance in a maximum number of 

 directions. 



Any animal type once evolved will extend itself immediately in 

 every direction as far as the natural barriers to its further dispersal 



