176 STUDIES IN LIFE AND SENSE. 



has, likewise, been to a slight extent modified by the migration 

 northwards of southern forms. In the life of South America we 

 perceive, on the other hand, the results of longer isolation and 

 greater specialisation. There the development of special forms of 

 life has accordingly progressed to a much greater extent than in 

 North America ; and the effect of a commingling of types has been 

 largely prevented by its relatively recent junction with Nearcticland. 

 As in Australia the lower types of quadruped life have been preserved 

 by the isolation of that area, so in South America the preservation 

 of the sloths, armadillos, and ant-eaters, and the development of 

 special forms of monkeys and other quadrupeds, are to be regarded 

 as the fruits of that separation which secures protection to lower and 

 comparatively defenceless life. 



A glance at some of the difficulties of distribution, and a reference 

 to the influence of migration upon the distribution of life, may draw 

 our consideration of this topic to a close. The progress of any 

 science from the stage wherein it formulates its beliefs in theory, to 

 that when its theories rise through cumulative proof into the higher 

 region of fact, is not accomplished without trial and tribulation. 

 Criticism, destructive and constructive, is the lot of every scientific 

 theory. But the earnest and unbiassed mind welcomes the criticism 

 wherein the trial of its beliefs is contained, as the honest mind gauges 

 the tenability of its beliefs by the residue, large or small, of solid fact 

 which it is able to collect after the critical assault upon its stronghold is 

 overpast. Of the science of distribution it may be said that its evil days 

 are fairly past. Critics it has had, and biological opinions may even 

 now be found to differ regarding the minor details of its constitution. 

 But the larger and more fundamental propositions of distributional 

 science remain untouched. They have passed out of the sphere of 

 discussion, and have taken their place amongst the stable facts 

 of the scientific system. It is necessary, however, to detail one or 

 two examples of the difficulties which may still disturb the com- 

 plexion of the scientific mind, and which are ever welcome to the 

 devotees of a science, since they afford the means whereby the weak 

 points and the unsettled problems of the science may be strengthened 

 and solved. 



Of such difficulties, then, let us specify a few instances, by way 

 o showing how readily their solution may, through careful considera- 

 tion, be obtained. Mr. Sclater has specified in a highly distinct 

 manner a few of the knotty points that await the student of distribu- 

 tion, and has thus afforded opportunity for the discussion of the 

 subject, and for their explanation or modification by the exercise of 

 scientific acumen and research. Taking the case of the lemurs 

 those curious quadrupeds usually classified as lower monkeys we 

 are presented with certain apparent anomalies in their distribution 



