OTHER NATURAL DIVISIONS. 2G1 



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 labour in this respect, in the Preface to his 

 Report upon the Insects Injurious to Vegetation. 



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 classifica- 

 tions, and attempted 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. 



Brandies 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 struc- 

 ture ; 



Families, by their form, as far as determined by struc- 

 ture; 



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. 



And yet there are other natural divisions which must 

 be acknowledged in a natural zoological system ; but 



