LEADING GROUPS OF EXISTING SYSTEMS 179 



the extent alluded to above. The practice prevailing since Linnasus, 

 of limiting the characteristics of species to mere diagnoses, has led to 

 the present confusion of our nomenclature, and made it often impos- 

 sible to ascertain what were the species the authors of such condensed 

 descriptions had before them. But for the tradition which has trans- 

 mitted, generation after generation, the knowledge of these species 

 among the cultivators of science in Europe, this confusion would be 

 still greater; but for the preservation of most original collections it 

 would be inextricable. In countries which, like America, do not enjoy 

 these advantages, it is often hopeless to attempt critical investigations 

 upon doubtful cases of this kind. One of our ablest and most critical 

 investigators, the lamented Dr. Harris, has very forcibly set forth the 

 difficulties under which American naturalists labor in this respect, 

 in the Preface to his Report upon the Insects Injurious to Vegeta- 

 tion?^ 



SECTION VII 

 OTHER NATURAL DIVISIONS AMONG ANIMALS 



Thus far I have considered only those kinds of divisions which 

 are introduced in almost all our modern classifications, and at- 

 tempted to show that these groups are founded in nature and ought 

 not to be considered as artificial devices invented by man to facilitate 

 his studies. Upon the closest scrutiny of the subject I find that these 

 divisions cover all the categories of relationship which exist among 

 animals, as far as their structure is concerned. 



Branches or types are characterized by the plan of their structure; 



Classes, by the manner in which that plan is executed, as far as 

 ways and means are concerned; 



Orders, by the degrees of complication of that structure; 



Families, by their form, as far as determined by structure; 



Genera, by the details of the execution in special parts; and 



Species, by the relations of individuals to one another and to the 

 world in which they live, as well as by the proportions of their parts, 

 their ornamentation, etc. 



«> [Pp. 1-8.] 



