273 



live the group or species and the less able to spread against 

 or resist the advancing tide of later developed and relatively 

 superior species. 



Although the more simply organised and primitive forms 

 of life are now so widely difíused, it is owing to their vast 

 antiquity that this has been attained, their enormous range 

 in time enabling them to overspread the globe by taking 

 advantage of the probably numerous geographical changes 

 that have occurred. 



The simpler and more primitive the species or group and 

 the more ancient its origin, the wider and more discontinuous 

 will be its range in space, for the more recently evolved and 

 more highly organised forms have a compact yet comparatively 

 restricted distribution at, or near, their evolutionary area, and 

 •exhibit Dominance or Superiority, a characteristic evidenced 

 by continuity of distribution, abundance of individuals, and 

 by a wealth of variation, which is an indication of the plasticity 

 of the organism and its power of adaptation to a great variety 

 of conditions, a power possibly due to the greater physiological 

 efficiency of its organs. 



The incessant encroachment upon the territories of the 

 less highly organised forms by the most adv^anced organisms, 

 implies and confirms that faunas and Iforas are, under normal 

 conditions, always in a state of slow and persistent transition, 

 imperceptible changes slowly but none the less surely going 

 on, for it is universally conceded that, prior to the life existing 

 at the present time, many previous forms had lived and been 

 dispersed over the globe, and as surely became extinct and 

 replaced by the improved races that have successively followed 

 them, and though every group of organisms has a certain area 

 or region in which for a period its metropolis is placed, yet the 

 site of .this aggregation is undoubtedly always undergoing a 

 slow and gradual displacement in position, but always in a 

 direction away from its original home or region in which it was 

 evolved, and to which it can never naturally return. 



This universal migratory movement is due not merely to 



the increase in numbers, but to the pressure of the subsequently 



evolved more advanced races which come in contact and 



competition with them, and will assuredly in course of time 



35 



