14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65. 



conditions of temperature and of humidity prevail, and Peripatus 

 finds its optimum conditions in somewhat warmer regions, the two> 

 most specialized types, Macro peripatus and Epiperipatus, are chiefly 

 characteristic of territory which is very warm, and more or less var- 

 iable both in temperature and in humidity. In other words, increasing 

 warmth of habitat is correlated with increased specialization of the 

 organism, and increased differentiation into subtypes, suggesting that 

 the original temperature under which the onychophores arose was 

 more comparable to the average temperature of the habitat of the 

 American genus occurring in the coolest situations than to that of the 

 habitat of any of the others. 



In the light of the preceding, and considered in connection with 

 what we know of the distribution of other animal types, the explana- 

 tion of the present distribution of this family in America appears to 

 be as follows : 



During the time tropical America was inhabited only by the primi- 

 tive Oroperipatus type, before the intrusion of the Peripatus type 

 from the east, the Cordillera had attained a height sufficient to pre- 

 vent the intrusion into that region of the newer and more specialized 

 forms originally developed under, and specialized for, an average 

 temperature somewhat higher than the optimum for the primitive 

 Oroperipatus. 



This new intrusive type, economically more efficient than the type 

 with which it came into competition, and better suited in every way to 

 meet existing conditions, extirpated the latter as far westward as the 

 crest of the Andes ; and so complete was this extirpation that only 

 three species of Oroperipatus are known to occur on the Atlantic side 

 of the divide, Oroperipatus bimbergi, from Amagatal and Guaduas, 

 Colombia ; Oroperipatus multipodes, from Rio Amago, Colombia ; 

 and Oroperipatus eiseni, from the Rio Purus, Brazil, though undoubt- 

 edly many more will be discovered in the future. Indeed the intrusive 

 type proved virile enough to enter the region west of the divide in 

 Colombia, Panama and Costa Rica, for we find Peripatus {Peripatus) 

 bouvieri at Boca del Monte, near Bogota, Colombia, and Peripatus 

 {Peripatus) ruber at Rancho Redondo, Costa Rica, as well as at Lino, 

 near Bouquete, in the Province of Chiriqui, Panama. 



At this epoch, when the Cordillera and the country to the west was 

 inhabited by the Oroperipatus type, and the country to the east by the 

 Peripatus type, South (and Central) America became separated from 

 Africa by the formation of the Atlantic Ocean, the accompanying 

 geological changes involving the disintegration of the Antillean 

 region, through submergence or otherwise, into the West India. 



