INTRODUCTION 5 



that may unite forms which morphologically and genetically 

 are not at all closely related, such as, to take extreme 

 instances, the limbless snakes and the lizards, the whales and 

 the fishes. 



II.— Geographical Distribution of Animals. 



Every phylum is represented in every great geographical 

 region of the globe, but this is not the case with every Class 

 and Order, still less with the smaller phyletic subdivisions. 

 Man and the animals domestic and parasitic that move in his 

 orbit excepted, each species in a state of nature has its own 

 restricted range, the limits of which though no doubt deter- 

 mined or maintained by conditions at present existing (such 

 as land-configuration, altitude, and climate ; enemies, com- 

 petitors, helpers, and hosts), must have been predetermined 

 and ordained by the physical conditions that obtained in an 

 earlier geological epoch. 



On the theory of Evolution the species at present existing 

 in any particular region of the world either (i) must be the 

 descendants of the species that existed there in the geological 

 epoch immediately preceding, or (2) must have immigrated 

 after some period of geological disturbance, or (3) may be an 

 association of aborigines and immigrants. 



Considering the subject from the first of these three points 

 of view. Huxley divided the world into four primary 

 zoological provinces, as follows : — 



(i) The Novozelanian Province, including New Zealand. 

 The only indigenous mammals are some bats and perhaps 

 rats ; and there is no evidence that any mammals existed in 

 New Zealand in earlier geological times. 



(2) 'Y\\s. Australian Province, including Australia,Tasmania, 

 and the Negrito Islands. Except for some bats and rats, and 

 perhaps a dog (which, however, may be a prehistoric immi- 

 grant of the human period, run wild), the only indigenous 

 mammals are Marsupials and Monotremes ; and the mam- 

 malian fossil remains of the immediately preceding geological 

 epoch are characteristically and overwhelmingly Marsupial. 



(3) The Austro - Columbian Province, including South 

 America and North America as far as Mexico. Here, 



