Chap. VI.] AFFINITIES AND GENEALOGY. 181 



capable of forming an independent judgment, and there- 

 fore need not here be further considered. 



"We can understand why a classification founded on 

 any single character or organ — even an organ so wonder- 

 fully complex and important as the brain — or on the high 

 development of the mental faculties, is almost sure to 

 prove unsatisfactory. This principle has indeed been tried 

 with hymenopterous insects ; but when thus classed by 

 their habits or instincts, the arrangement proved thor- 

 oughly artificial. 3 Classifications may, of course, be based 

 on any character whatever, as on size, color, or the ele- 

 ment inhabited ; but naturalists have long felt a profound 

 conviction that there is a natural system. This system, 

 it is now generally admitted, must be, as far as possible, 

 genealogical in arrangement — that is, the co-descendants 

 of the same form must be kept together in one group, sep- 

 arate from the co-descendants of any other form ; but if 

 the parent-forms are related, so will be their descendants, 

 and the two groups together will form a larger group. 

 The amount of difference between the several groups — 

 that is, the amount of modification which each has under- 

 gone — will be expressed by such terms as genera, families, 

 orders, and classes. As we have no record of the lines of 

 descent, these lines can be discovered only by observing 

 the degrees of resemblance between the beings which are 

 to be classed. For this object numerous points of resem- 

 blance are of much more importance than the amount of 

 similarity or dissimilarity in a few points. If two lan- 

 onia^es were found to resemble each other in a multitude 

 of words and points of construction, they would be uni- 

 versally recognized as having sprung from a common 

 source, notwithstanding that they differed greatly in some 

 few words or points of construction. But with organic 

 beings the points of resemblance must not consist of 



3 Westwood, ' Modern Class, of Insects,' vol. ii. 1840, p. 87. 



