CHAP. xxTii.] SU.MMARY AND CONCLUSION. 541 



Primates had, even at that early epoch, diverged into distinct 

 series, so that we must probably look back to the secondary 

 period for the ancestral form from which the entire order was 

 developed. 



Cliiroptera. — These are also undoubtedly very ancient. The 

 most generalised forms — the Vespertilionidpe and Noctilionid^ — 

 are the most widely distributed ; while special types have arisen 

 in America, and in the Eastern Hemisphere. Eemains found in 

 the Upper Eocene formation of Europe differ little from species 

 still living in the same countries ; so that we can form no con- 

 jecture as to the origin or migration of the group. Their power 

 of flight would, however, enable them rapidly to spread over 

 all the great continents of the globe. 



Insectivora. — This very ancient group, now probably verging 

 towards extinction, appears to have originated in the Northern 

 continent, and never to have reached Australia or South America. 

 It may, however, have become extinct in the latter country 

 owing to the competition of the numerous Edentata. The In- 

 sectivora now often maintain themselves amidst more bighly 

 developed forms, by means of some special protection. Some 

 burrow in the earth, — like the moles ; others have a spiny cover- 

 ing, — as the hedgehogs and several of the Centetidte ; others 

 are aquatic, — as the Potamogcdc and the desman ; others have a 

 nauseous odour, — as the shrews ; while there are several which 

 seem to be preserved by their resemblance to higher forms, — as 

 the elephant-shrews to jerboas, and the tupaias to squirrels. 

 The same need of protection is shown by the numerous Insecti- 

 vora inhabiting IMadagascar, where the competing forms are 

 few ; and by one lingering in the Antilles, where there are 

 hardly any other mammalia. 



(7o?'MM'o?"«.— Although perhaps less ancient than the preced- 

 ing, this form of mammal is far more higlily organised, and 

 from its earliest appearance appears to have become dominant 

 in the world. It would therefore soon spread widely, and 

 diverge into the various specialised types represented by exist- 

 ing families. Most of these appear to have originated in the 

 Eastern Hemisphere, the only Caruivora occurring in North 



