Classification. 1951 



some naturalists it may be most familiar. Instead of being applied to 

 a single species or group, made use of as a standard to which other 

 species or groups are to be compared, it is here used to signify a cer- 

 tain plan or model, on which a large number of species are con- 

 structed, and whose characteristic peculiarities show themselves 

 throughout the whole series, notwithstanding the great variety which 

 the different adaptations may occasion : a similar constancy of cha- 

 racter through a certain number of the species included in the more 

 extended type, of course will constitute them a subordinate type. 

 Then the course to be pursued in the construction of a natural system 

 (that is, so far natural as possible, by forming every group according 

 to the true affinities of the species which it contains) is, by an ex- 

 tended and rigid investigation, to search out the characters by which 

 the natural affinities are indicated ; and in descending from the higher 

 divisions to the lower, to make no use of the adaptive characters, un- 

 til we are certain that the essential characters (that being the term 

 most generally adopted to imply those by which the type may be re- 

 cognized) are completely exhausted; and then, having fully ascer- 

 tained the natural subdivisions of the group to which our attention 

 has been directed, to dispose them in such different degrees of rank, 

 and in such an arrangement, as shall seem most convenient for pur- 

 poses of description, and, from the judicious manner in which it is ef- 

 fected, be likely to meet with general approval and adoption among 

 those engaged in similar researches. 



Commencing, in this course of investigation, with the largest and 

 most extensive divisions, it will, it is manifest, be necessary to disre- 

 gard, until a late period, a great number of characters, which, from 

 their conspicuous appearance, are such as might otherwise have been 

 the first to attract our notice, and have been the stumbling-blocks to 

 which most of the errors of the old systematists owe their origin ; and 

 to proceed to classify upon peculiarities of structure, which, from their 

 constancy and independence of adaptive modifications, we have ascer- 

 tained to belong to the type. It is almost impossible to lay down 

 rules for the pursuit of such a search ; the characters in question may 

 be obvious, maybe apparently trifling; in animals of more complex 

 organization, it seems hardly necessary to add that they can seldom 

 be external. They must, of course, be first looked for in those organs 

 whose offices are of the highest importance, in the performance of the 

 vital functions of the creature, and, as has before been observed, it is 

 upon these that the more extensive groups have most generally been 

 founded ; but those beautiful laws of correlation, everywhere pervading 



