INSESSORIAL BIRDS, ^ 237 



divisions will all conform to one or another of a certain set of plans 

 of development, which set of plans or tendencies will equally be 

 found to regulate the variations of every other known type, thus 

 indicating a general order in nature and a certain uniformity in the 

 methods by which the most varied results are produced. Not only 

 does the variety to be called forth under each type or sub-type 

 remain as a subject for observation, but we soon learn that a general 

 type of structure being given, we may have the several plans of 

 dfevelopmentj which give the definite number, repeated in several 

 different grades or degrees of development, for the number of which 

 we know of no definite law, so as in many cases greatly to increase 

 the number of organic forms. Now we believe it is generally agreed 

 that all the organisms of which the remains have been recognized in 

 the strata of the globe conform to the grand types of. animal and 

 vegetable structure now known upon the earth. It is therefore the 

 wildest conjecture to suppose that those we do not know may exhibit 

 altogether new and distinct general plans of structure, and as to 

 minor differences they find their place in perfect consistency with 

 regularity of plan. "We cannot help regarding Mr. Wallace's esti- 

 mate of the numbers of extinct creatures as considerably exaggerated^ 

 but whatever may be thought on this subject, we must judge of the 

 successive extinct races by the traces of them which remain, and 

 these as clearly indicate a definite plan in Nature, and as certainly 

 prove the uniformity of that plan as a whole, through all periods, as^ 

 could be desired by the most scrupulous weigher of evidence. 



Mr. Wallace's second argument is thus stated : " This system 

 absolutely places limits to the variety and extent of creation ; for it 

 is said that every group can only contain five sub-groups, and the 

 number of gradations of groups is fixed. For instance, in a family 

 there can be only five true genera, and again in each group, five sub- 

 genera. In the Psittacidae, therefore, there can be but twenty-five 

 generic forms, and when those are all known, not only is it declared 

 impossible to discover a new one, but it is also asserted that no other 

 can possibly ever have existed and become extinct. This is the 

 logical deduction from any system of definite number in Natural 

 History, and it is one that should convince every person of the false 

 basis on which all such systems rest." I do not know how far this 

 reasoning may apply against Mr. Swainson's system, or some modes 

 of stating it, but I feel very confident that it does not apply to all 

 theories of classification implying the occurrence of definite num- 



