158 STUDIES IN LIFE AND SENSE. 



so likewise are the Insectivora belonging to the curious genus 

 Soknodon. Two species of Solenodon occur, one in Cuba, the other 

 in Hayti. These animals are allied to the Madagascar " tenrecs." 

 They possess an extremely elongated nose, a long and scaly tail, and 

 powerful claws. The fur is coarse, and the teeth are peculiar in some 

 respects. 



The entire zoological history of the West Indian Islands tends to 

 show their distinctness as a biological region. Their fauna bears a 

 decidedly Neotropical character in its essential details, but it is like- 

 wise a fauna which has undergone extensive modification through a 

 Jong separation from the ancient mainland of which these islands 

 once formed part. 



The biological divisions of the globe having thus been detailed, 

 the task of investigating the causes which have wrought out the 

 existing distribution of life on its surface yet remains. These pre- 

 liminary studies form the material facts whereupon we may erect a 

 solid hypothesis concerning the means whereby the living popula- 

 tion of the earth has been modified, assorted, and arranged. We 

 may accordingly marshal the facts in due order, that we may connect 

 them by a theoretical bond using hypothesis, thus legitimately, as a 

 guide to the discovery of truth. 



Having thus summarised the chief facts relating to the dis- 

 tribution of the higher animals on the surface of the globe, and 

 having indicated the boundaries of the six great regions into which, 

 from a consideration of the distribution of life, the biologist divides 

 the land areas of the earth, we may now enter upon the con- 

 sideration of the explanations which biology is prepared to afford 

 of the facts in question. It is necessary to bear in mind the 

 cardinal fact that only two theories are possible respecting the 

 distribution of life on the earth ; as, indeed only two explanations 

 may be offered concerning any other cosmical phenomena, whether 

 relating to the world of life or to that of inorganic matter. In 

 other words, we must either assume, in the first place, with re- 

 gard to the distribution of life, or to the origin of species itself, 

 that a supernatural, and therefore inexplicable, fiat in the beginning 

 of things, created each species separately and independently, and 

 placed it directly or indirectly in its special locality or home; 

 or, secondly, we may elect to believe, on the theory of evolution, 

 that the varied tribes of living beings are the descendants of pre- 

 existing species ; that variation and modification constitute great 

 and continuously operating factors in moulding the living form ; 

 that species extend or limit their range of habitat according to 

 the facilities or obstacles presented by their surroundings ; and 

 lastly, that physical and geological changes of the earth's surface 

 are continually operating and influencing at once the relations 



