CHAP. XXIII.] 
SUMMARY 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. 
Chiroptera . — These are also undoubtedly very ancient. The 
most generalised forms — the Vespertilionidee and Noctilionidse — 
are the most widely distributed ; while special types have arisen 
in America, and in the Eastern Hemisphere. Remains found in 
the Upper Eocene formation of Europe differ little from species 
still living in the same countries ; so that w T e 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. 
Inseetivora . — 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 highly 
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 Centetidse ; others 
are aquatic, — as the Potamogale 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 Madagascar, where the competing forms are 
few; and by one lingering in the Antilles, where there are 
hardly any other mammalia. 
Carnivora . — Although perhaps less ancient than the preced- 
ing, this form of mammal is far more highly 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 Carnivora occurring in North 
