NO. I DISTRIBUTION OF THE ONYCHOPHORA CLARK 3 



This means that many barriers have operated as a check to their 

 dispersal which are readily passed by the great majority of the other 

 terrestrial types, both invertebrate and vertebrate, and suggests that 

 the facts presented by the distribution of the onychophores possesses 

 exceptional value. 



Although existing within very narrow physical limits, the onycho- 

 phores are in certain ways more independent of their immediate sur- 

 roundings than the great majority of invertebrates, for they are 

 predacious, and apparently feed upon any organisms small enough 

 for them to overcome. This renders them quite independent of the 

 distribution of the plant species, which determines the distribution 

 of many insects, and which in turn is governed to a large extent by 

 the underlying geology of the regions in which the plants occur. 



THE THERMAL DISTRIBUTION OF THE ONYCHOPHORES 

 The mean annual temperature of the portions of the world in- 

 habited by the onychophores varies from 50 to 8o° F. (10.00 to 

 26.67 C), though certain forms occur locally in average, tempera- 

 tures slightly in excess of both of the extremes given. So far as we 

 are able to calculate from the estimated temperatures of their habitats, 

 most of the species occur between the limits of 6o° and 70° F. ( 15.56 

 and 21.11 C), which appears to be the optimum temperature range 

 for the group, suggesting that it was between these temperatures that 

 these animals originated. 



A critical study of the recent crinoids shows that their optimum 

 temperature is between 55° and 65° F. (12.78° and 18.33° C.), and I 

 have suggested that it was probably within this temperature range 

 that the post-palaeozoic crinoid fauna, at least, attained its greatest 

 development. 1 



Combining the data deduced from the study of these two groups, 

 the one marine, the other terrestrial, we find a coincidence of the 

 optimum conditions for both between 6o° and 65° F. (15.56° and 

 18.33° C). 



GENERAL FEATURES OF THE DISTRIBUTION OF THE 

 ONYCHOPHORES 



The most striking feature of the geographical distribution of the 

 onychophores as we know it today is the restriction of all the species 



*Une etude philosophique de la relation entre les crino'ides actuels et la 

 temperature de leur habitat. Bulletin de lTnstitut Oceanographique (Fonda- 

 tion Albert I er , Prince de Monaco), No. 294, 20 Juin, 1914. 



