_|78 MAMMALS. PHYLUM CHORDATA 



All the British species belong to a section of the Order, the 

 Microcheiroptera, which feed on insects caught on the wing and 

 have cheek teeth much like those of the Insectivora. There are 

 twelve British species, but only two of these, the pipistrelle 

 [Pipisirellus pipistrellus) and the long-eared bat (Plecotus auritus) 

 are widely distributed. In some species insects caught on the wing 

 are transferred to a pouch, formed by the forwardly-turned tail, 

 for storage. 



PRIMATES 



The primates resemble the Insectivora so closely that there 

 has long been, and still is, controversy as to whether one family, 

 the tree-shrews or Tupaiidae, are best placed in one group or 

 the other. These are small creatures from the Eastern tropics 

 and differ from the typical insectivores in a number of features 

 in which they agree with the primates. Primates are in fact 

 fundamentally arboreal insectivores ; they retain a number of 

 primitive features such as tubercular cheek teeth, the clavicle, 

 separate radius and ulna, plantigrade gait and five digits, but 

 show a number of progressive specialisations. The orbit is sur- 

 rounded by bone, the postorbital process of the frontal meeting 

 an upgrowth from the jugal, there is a gradual reduction in the 

 relative extent of the preorbital region of the skull, the claws 

 become flat nails, and both hallux and pollex are typically 

 opposable, so that first the branches of trees and then portable 

 objects can be grasped. It has indeed been suggested that the 

 development of the thumb was the most important step in the 

 evolution of the order, for by its means, combined with stereo- 

 scopic vision, objects can be examined and so thought becomes 

 directed to a particular thing and more readily used as the 

 material for natural selection. It is relevant to this hypothesis 

 that the parrots, which also use the feet as hands for holding 

 and examining objects, have relatively the largest brains, and the 

 largest cerebral hemispheres, of all birds. However that may be, 

 the chief distinction of the primates is their large brains and their 

 large and convoluted hemispheres. With this goes an increase 

 in the carotid circulation. 



So far as is known, the only primate ever to inhabit these islands 

 is man, and the present species. Homo sapiens, probably arrived 

 about fifty thousand years ago. While man retains such primitive 



