MACKIE — FIRST TEACES OF THE SUCCESSION OF LIFE, 345 



allow themselves to get confased with the variety of teiTQS used by 

 different authors to designate the same or nearly the same classes of 

 animals or plants. Such differences are no more than the natm'al 

 results of the attempts to found a perfect system of classification 

 while necessarily beginning to make that effort with imperfect 

 materials, which through many deficiencies in our knowledge present 

 also great gaps and voids in the desired continuity of the order of 

 arrangement of organized beings. By degrees such gaps are filled 

 up in the progi^ess of our investigations, and by the acquirement of 

 additional knowledge of the structural character of known species, 

 or the discovery of new forms. 



Under the scientific classification presented in further detail in 

 Table II., existing forms of animals can be more or less hannoniously 

 arranged. It may be regarded as that generally received, the terms 

 being those ordinarily in use by the principal writers ; and in it we 

 have included the latest revisions and amendments in the arrange- 

 ment of the Mammalia by Professor Owen, whose indefatigable 

 researches, skilful observation, and perspicuous deductions have long 

 since placed him in the foremost rank of naturahsts, whether past or 

 present. 



By him this most important class has been primarily grouped, 

 according to the characters of the brain, into four principal di^^sions, 

 which thus displayed also exhibit their comparative intellectual 

 capacities. 



For the complete gTouping and arrangement of the animal and 

 vegetable kingdoms it is necessary that all those fossil forms, often so 

 widely different from those existant, which palaeontology has added, 

 and is still daily adding, to the fauna and flora of our planet in its 

 completeness, should be included and brought into one and the same 

 harmonious grouping. Thus does every new fonn exhumed from the 

 great cemetery of the Past add some new hnk to or produce some fresh 

 deviation from our latest and most complete results of arrangements. 

 It is, however, not a httle curious to find the rehcs of past ages sup- 

 plying the gaps and deficiencies of the creation around us, and form- 

 ing the links between what were previously considered aberrant and 

 abnormal conditions ; every step of progTess adding to the beauty, 

 harmony, consistency, and unity of the great plan of creation. 



