534 DE. P. CHALMERS MITCHELL ON" THE 



6. Prosimi^e. 



There are suggestions that the radius on which the Prosimife lie is confluent at first 

 with the Ungulate radius or at least parallel with it, but the group has not moved far 

 from the centre, and certainly leaves the Ungulate radius before the specialisation of 

 the Perissodactyla. 



7. SlMLE. 



The radius of this group is close to that of the Prosimiae and Ungulata, but its least 

 specialised members have not moved so far from the common centre as the lowest 

 Ungulates and Prosimise, whilst the more specialised members move outwards along 

 their own radius. 



8. RODENTIA. 



A distinct radius, along which the more specialised members have moved far from 

 the centre. 



9. Insectivora. 



10. Chiroptera. 



11. Carnivora. 



These three groups, so far as their lower members are concerned, have not moved 

 far from the common centre. The higher members show a similar mode of speciali- 

 sation, which consists of reduction of the hind-gut, and whilst probably, on the evidence 

 of the intestinal tract, they would be placed close together, the evidence is not 

 conclusive, as it may well be supposed that the reduction could have taken place 

 independently. 



General Conclusion. 



The positive systematic inferences to be drawn from this assemblage of anatomical 

 data are obviously extremely limited, but I am of opinion that a similar scrutiny of any 

 other assemblage of data, conducted so as to exclude in the same way the drawing of 

 inferences based on the common possession of primitive characters, would give equally 

 limited results. Approach to correct classiiication, based on affinity, can be made only 

 by combining the few positive results that examination of each series of anatomical 

 data would yield. On the other hand, it appears to me that an examination such as I 

 have endeavoured to make in this memoir has an important bearing on the theory of 

 evolution. We have no information as to why the different groups of animals came 

 to occupy the particular radiating streams of differentiation on which, with regard to 

 any particular set of organs, they are found to lie. The initial deciding factor may 

 have been direct adaptation, the selection of small variations or of large variations, or 

 correlation with some such adaptation or selection. But once any set of animals has 

 come to occupy a particular radius, then, in that respect, its possible range of variation 



