THE STUDY OF BIOLOGY. 31 



impassable gulf to migrating forms, has -kept the original quadruped- 

 life of that island-continent free, separate, and unmingled with the 

 higher types of life evolved since Triassic and Oolitic times. Thus 

 do we answer the question, " Where is the kangaroo found ? " 



The remaining question, " How has it come to be what it is ? " 

 or, in other words, " How has it assumed its present place in the 

 organic series ? " has been answered in greater part by the preceding 

 observations. If the first quadruped population of Australia was, as 

 we know it to have been, of marsupial nature, our existing kangaroo 

 must be the descendant of pre-existing species. Laws of descent, 

 affected by variation, have unquestionably produced and evolved the 

 existing kangaroo from ancestors more or less resembling itself. 

 This much is clear, at least that although the exact lines of descent 

 and variation of the marsupial families of to-day are as yet un- 

 determined, the great principle of descent through variation from 

 pre-existing species, remains, not a theory merely, but an inferred 

 and unmistakable fact from the circumstances of the case. As the 

 various opossums now inhabiting America are the descendants of 

 the one or more primitive species which first colonised the New 

 World, so the varied marsupial life of Australia is the legitimate 

 outcome, through variation, of the primitive quadrupeds which first 

 peopled that strange land in the old Triassic days. As Professor 

 Flower has remarked, even the likeness between the feet of 

 marsupials is too close to admit of any doubt of their derived 

 relationship, " of inheritance from a common ancestor." And the 

 causes which have produced the striking likeness of this one feature 

 in marsupial history are simply those which have also evolved, from 

 a common origin, the varied features and new offshoots which mark 

 the marsupial life of to-day. 



The somewhat extended survey thus taken of the means and 

 methods of biological study obviates any necessity for extending 

 more fully our researches into the remaining characteristics of modern 

 biology. What remains to be said on this latter head may, however, 

 be shortly summed up in the light of previous remarks. Natural 

 history science, as prosecuted of old, was a mere collection of 

 . descriptions of species. It was a science in which the search after 

 new species, merely for the sake of adding to the number of known 

 forms, was the paramount aim of the zoologist and botanist. 

 Classifications grew apace; but the relations of one species to 

 another, of group to group, or the general plan upon which the 

 animal world was constructed and organised, were either undreamt 

 of as subjects of study, or were cursorily dismissed from scientific 

 view. We have but to open a volume of natural history lore of the 

 past decade of zoology to realise the truth of this statement. We 

 may readily perceive that attention to outside characters and to the 



