10 PRELIMINARY INQUIRIES. 



Agassiz, again, saj's, " Nothing can be more striking to the observer than the fact that animals, 

 though endowed with the power of locomotion, remain within tixcd bounds in their geographical 

 distribution, although an unbounded field for migration is open to them in all directions over land, 

 through the air, and through the waters. And no stronger argument can be introduced to show 

 that living beings are endowed with their power of locomotion to keep within general boundaries 

 rather than to spread extensively." * "We know well enough what he means by this paradox ; 

 although, if we were inclined to be critical, we might call it rather a Hibernian definition of 

 the purposes of the organs of locomotion, to say that limbs are given us to enable us to stay 

 at home. 



None of these authors can mean that there is any special attraction for the fauna in the solum 

 of the province. The history of the glacial epoch furnishes us with a thousand instances to the 

 contrary. As the cold retired from the Equator, the glacial inhabitants (produced, as I believe, 

 under its influence) followed in its footsteps. The law they speak of must apply not to the place 

 but to its conditions. 



The hj-pothesis which I offer seems to meet all the requirements of the case. Under it, 

 the provinces are preserved special, not by any mysterious erooyri, or peculiar law which prevents 

 their inmates from using their limbs for going abroad, but simply, in the first place, by the inertia, 

 or instinctive regard for personal ease, which leads every creature to remain where it is while 

 it is comfortable, and so not to pass beyond the bounds for which it was originally fitted and best 

 adapted, into others less suited for it. And, in the next place, when by geological changes, in- 

 sufficiency of food for growing numbers, or other extraneous causes, it is reluctantly diiven out 

 or compelled to pass beyond its natural province, the province is still preserved special either 

 by the death of those which have gone beyond it, or by their transformation (in consequence of 

 their having passed under new conditions of life,) into something else — into a new phase of their 

 old form — in a word, into new sjiecies, more or loss distant from the original type according to the 

 character of the new conditions. 



This hypothesis also accords sufficiently well with what we know of the history of species 

 during past geological epochs. If the common belief be well foimded that our globe at one stage 

 of its existence was a ball of incandescent matter, which for long went on gradually cooling, 

 it must follow that the more such internal heat made itself felt at the surface, the more uniform 

 the temperature and climate in every country on the face of the earth must have been, and the less 

 the amount of variation in the conditions of life upon it. 



As the internal heat diminished, the more woidd the surface become liable to the extraneous 

 influence of heat from the sun, or to unequal degrees of radiation from land and sea; and as 

 their proportions and arrangement varied, the greater would be the variety of the conditions of 

 life upon the surface of the globe and the more frequently would changes in them take place. 

 Now the theoretical result of such a state of things upon the production of species accordin"- to 

 the laws which my hj-pothcsis presupposes, would be, that during the earlier periods of the history 

 of the globe, the number and variety of forms of life would be more uniform and fewer in number, 

 and during the later periods when the amount of internal heat was diminishing, the forms of life 

 WDuld be more varied and numerous. The formation of new species being, according to my 

 theory, dependent upon the old ones encountering a new condition of life, where there was only 



* Agassiz, op. cit. i>. 13. 



